{"id":19183,"date":"2025-07-07T01:30:05","date_gmt":"2025-07-06T18:30:05","guid":{"rendered":"https:\/\/www.ckconitsha.com\/vn\/?p=19183"},"modified":"2025-07-08T08:05:02","modified_gmt":"2025-07-08T01:05:02","slug":"huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat","status":"publish","type":"post","link":"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/","title":{"rendered":"H\u01b0\u1edbng d\u1eabn c\u00e1ch vi\u1ebft v\u00e0 c\u00e1ch \u0111\u1ecdc s\u1ed1 21 s\u1ed1 la m\u00e3 ch\u00ednh x\u00e1c nh\u1ea5t"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_79_2 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Huong_dan_ve_cach_doc_chinh_xac_so_21_cua_La_Ma\" >H\u01b0\u1edbng d\u1eabn v\u1ec1 c\u00e1ch \u0111\u1ecdc ch\u00ednh x\u00e1c s\u1ed1 21 c\u1ee7a La M\u00e3<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Cach_viet_21_so_La_Ma_theo_quy_tac_bat_bien\" >C\u00e1ch vi\u1ebft 21 s\u1ed1 La M\u00e3 theo quy t\u1eafc b\u1ea5t bi\u1ebfn<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Mot_so_loai_bai_tap_tren_so_21_o_Rome_la_pho_bien_trong_bai_kiem_tra\" >M\u1ed9t s\u1ed1 lo\u1ea1i b\u00e0i t\u1eadp tr\u00ean s\u1ed1 21 \u1edf Rome l\u00e0 ph\u1ed5 bi\u1ebfn trong b\u00e0i ki\u1ec3m tra<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Mau_1_Them_so_21_cua_La_Ma\" >M\u1eabu 1: Th\u00eam s\u1ed1 21 c\u1ee7a La M\u00e3<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Mau_2_Xac_dinh_so_21_trong_chuoi_da_cho\" >M\u1eabu 2: X\u00e1c \u0111\u1ecbnh s\u1ed1 21 trong chu\u1ed7i \u0111\u00e3 cho<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Mau_3_So_sanh_so_luong_Roman_voi_21\" >M\u1eabu 3: So s\u00e1nh s\u1ed1 l\u01b0\u1ee3ng Roman v\u1edbi 21<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Mau_4_Doc_va_viet_so_binh_thuong_cho_banh_rang_La_Ma_va_nguoc_lai_21\" >M\u1eabu 4: \u0110\u1ecdc v\u00e0 vi\u1ebft s\u1ed1 b\u00ecnh th\u01b0\u1eddng cho b\u00e1nh r\u0103ng La M\u00e3 v\u00e0 ng\u01b0\u1ee3c l\u1ea1i 21<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#De_xuat_mot_so_bai_tap_ve_21_so_La_Ma_de_giup_tre_thuc_hanh_hieu_qua\" >\u0110\u1ec1 xu\u1ea5t m\u1ed9t s\u1ed1 b\u00e0i t\u1eadp v\u1ec1 21 s\u1ed1 La M\u00e3 \u0111\u1ec3 gi\u00fap tr\u1ebb th\u1ef1c h\u00e0nh hi\u1ec7u qu\u1ea3<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Bai_tap_1\" >B\u00e0i t\u1eadp 1<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Bai_tap_2\" >B\u00e0i t\u1eadp 2<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Bai_tap_3\" >B\u00e0i t\u1eadp 3<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Bai_tap_4\" >B\u00e0i t\u1eadp 4<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Bai_tap_5\" >B\u00e0i t\u1eadp 5<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Bai_tap_6\" >B\u00e0i t\u1eadp 6<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-15\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Bi_quyet_de_giup_em_be_cua_ban_nho_so_21_cua_nguoi_La_Ma_don_gian\" >B\u00ed quy\u1ebft \u0111\u1ec3 gi\u00fap em b\u00e9 c\u1ee7a b\u1ea1n nh\u1edb s\u1ed1 21 c\u1ee7a ng\u01b0\u1eddi La M\u00e3 \u0111\u01a1n gi\u1ea3n<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-16\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Hay_nho_quy_tac_viet_21_Roman\" >H\u00e3y nh\u1edb quy t\u1eafc vi\u1ebft 21 Roman<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-17\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Thuc_hanh_thuong_xuyen_voi_21\" >Th\u1ef1c h\u00e0nh th\u01b0\u1eddng xuy\u00ean v\u1edbi 21<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-18\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Choi_tro_choi_voi_21_nguoi_La_Ma\" >Ch\u01a1i tr\u00f2 ch\u01a1i v\u1edbi 21 ng\u01b0\u1eddi La M\u00e3<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-19\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Phan_biet_cac_ky_tu_de_tranh_su_nham_lan\" >Ph\u00e2n bi\u1ec7t c\u00e1c k\u00fd t\u1ef1 \u0111\u1ec3 tr\u00e1nh s\u1ef1 nh\u1ea7m l\u1eabn<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-20\" href=\"https:\/\/www.ckconitsha.com\/vn\/huong-dan-cach-viet-va-cach-doc-so-21-so-la-ma-chinh-xac-nhat\/#Thuc_hanh_viet_va_dat_cau_hoi_ve_so_La_Ma_21\" >Th\u1ef1c h\u00e0nh vi\u1ebft v\u00e0 \u0111\u1eb7t c\u00e2u h\u1ecfi v\u1ec1 s\u1ed1 La M\u00e3 21<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n<\/p>\n<p>L\u00e0m th\u1ebf n\u00e0o \u0111\u1ec3 \u0111\u1ecdc v\u00e0 vi\u1ebft 21 s\u1ed1 La M\u00e3 c\u00f3 v\u1ebb \u0111\u01a1n gi\u1ea3n, nh\u01b0ng nhi\u1ec1u tr\u1ebb em khi l\u00e0m b\u00e0i t\u1eadp v\u1ec1 nh\u00e0 r\u1ea5t d\u1ec5 nh\u1ea7m l\u1eabn v\u00e0 l\u00e0m sai. V\u00ec v\u1eady, b\u00e0i vi\u1ebft sau \u0111\u00e2y s\u1ebd h\u01b0\u1edbng d\u1eabn c\u00e1ch em b\u00e9 c\u1ee7a b\u1ea1n bi\u1ebft c\u00e1ch \u0111\u1ecdc, vi\u1ebft v\u00e0 l\u00e0m b\u00e0i t\u1eadp v\u1ec1 nh\u00e0 21 c\u1ee7a s\u1ed1 La M\u00e3 \u0111\u1ec3 n\u00f3 c\u00f3 hi\u1ec7u qu\u1ea3.<\/p>\n<p>                                                                    <img decoding=\"async\" src=\"https:\/\/external-content.duckduckgo.com\/iu\/?u=https:\/\/vnmedia2.monkeyuni.net\/upload\/web\/img_default\/monkey3.png\" alt=\"\"><\/p>\n<p class=\"title\">H\u00e0ng tri\u1ec7u tr\u1ebb em \u0111\u00e3 ph\u00e1t tri\u1ec3n c\u00e1c k\u1ef9 n\u0103ng ng\u00f4n ng\u1eef c\u1ee7a ch\u00fang th\u00f4ng qua c\u00e1c \u1ee9ng d\u1ee5ng h\u1ecdc t\u1eadp c\u1ee7a kh\u1ec9<\/p>\n<p class=\"description\">\u0110\u0103ng k\u00fd ngay \u0111\u1ec3 \u0111\u01b0\u1ee3c t\u01b0 v\u1ea5n mi\u1ec5n ph\u00ed v\u1ec1 c\u00e1c s\u1ea3n ph\u1ea9m v\u00e0 tuy\u1ebfn h\u1ecdc h\u1ecdc cho tr\u1ebb em.<\/p>\n<p>                                                                            *Vui l\u00f2ng ki\u1ec3m tra t\u00ean \u0111\u1ea7y \u0111\u1ee7 c\u1ee7a b\u1ea1n *Vui l\u00f2ng ki\u1ec3m tra s\u1ed1 \u0111i\u1ec7n tho\u1ea1i \u0111\u1ec3 \u0111\u01b0\u1ee3c t\u01b0 v\u1ea5n mi\u1ec5n ph\u00ed<\/p>\n<h2 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Huong_dan_ve_cach_doc_chinh_xac_so_21_cua_La_Ma\"><\/span>H\u01b0\u1edbng d\u1eabn v\u1ec1 c\u00e1ch \u0111\u1ecdc ch\u00ednh x\u00e1c s\u1ed1 21 c\u1ee7a La M\u00e3<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p dir=\"ltr\">V\u1ec1 vi\u1ec7c \u0111\u1ecdc, s\u1ed1 21 Roman c\u00f3 c\u00f9ng c\u00e1ch v\u1edbi s\u1ed1 21 trong t\u1ef1 nhi\u00ean. M\u1ecdi ng\u01b0\u1eddi s\u1ebd \u0111\u1ecdc l\u00e0 &#8220;hai m\u01b0\u01a1i m\u1ed1t&#8221;. Khi \u0111\u1ecdc 21 s\u1ed1 La M\u00e3, tr\u1ebb em v\u00e0 cha m\u1eb9 s\u1ebd ch\u00fa \u00fd \u0111\u1ebfn c\u1ea5u tr\u00fac c\u0169ng nh\u01b0 c\u00e1c ch\u1eef s\u1ed1 La M\u00e3 xu\u1ea5t hi\u1ec7n trong 21 v\u00e0 sau \u0111\u00f3 \u0111\u1ecdc. C\u1ee5 th\u1ec3:<\/p>\n<p dir=\"ltr\"><img decoding=\"async\" class=\"lazyload\" src=\"https:\/\/external-content.duckduckgo.com\/iu\/?u=https:\/\/vnmedia2.monkeyuni.net\/upload\/web\/img\/1-21-so-la-ma.png\" alt=\"L\u00e0m th\u1ebf n\u00e0o \u0111\u1ec3 \u0111\u1ecdc s\u1ed1 21 th\u00edch? (Ngu\u1ed3n h\u00ecnh \u1ea3nh: B\u1ed9 s\u01b0u t\u1eadp Internet)\" width=\"100%\"><\/p>\n<ul>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">X mang gi\u00e1 tr\u1ecb 10 v\u00e0 21 s\u1ebd c\u00f3 di\u1ec7n m\u1ea1o hai l\u1ea7n c\u1ee7a X.<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">T\u00f4i mang l\u1ea1i gi\u00e1 tr\u1ecb c\u1ee7a 1, \u0111\u00fang v\u1ecb tr\u00ed sau xx (20)<\/p>\n<\/li>\n<\/ul>\n<p dir=\"ltr\">C\u00f3 th\u1ec3 th\u1ea5y r\u1eb1ng s\u1ed1 21 trong Roman c\u00f3 c\u00e1ch \u0111\u1ecdc r\u1ea5t \u0111\u01a1n gi\u1ea3n, kh\u00f4ng qu\u00e1 kh\u00f3.<\/p>\n<h2 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Cach_viet_21_so_La_Ma_theo_quy_tac_bat_bien\"><\/span>C\u00e1ch vi\u1ebft 21 s\u1ed1 La M\u00e3 theo quy t\u1eafc b\u1ea5t bi\u1ebfn<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p dir=\"ltr\">C\u00f3 th\u1ec3 th\u1ea5y c\u00e1ch \u0111\u1ecdc 21 s\u1ed1 La M\u00e3 kh\u00f4ng qu\u00e1 kh\u00f3, v\u00ec v\u1eady theo c\u00e1ch t\u01b0\u01a1ng t\u1ef1, v\u1ec1 c\u00e1ch vi\u1ebft s\u1ed1 La M\u00e3 21 c\u0169ng r\u1ea5t d\u1ec5 d\u00e0ng. S\u1ed1 21 trong La M\u00e3 l\u00e0 XXI. <\/p>\n<p dir=\"ltr\"><img decoding=\"async\" class=\"lazyload\" src=\"https:\/\/external-content.duckduckgo.com\/iu\/?u=https:\/\/vnmedia2.monkeyuni.net\/upload\/web\/img\/2-21-so-la-ma.jpg\" alt=\"Vi\u1ebft s\u1ed1 21 La M\u00e3 (Ngu\u1ed3n: B\u1ed9 s\u01b0u t\u1eadp Internet)\" width=\"100%\"><\/p>\n<p dir=\"ltr\">Do \u0111\u00f3, tr\u1ebb em s\u1ebd kh\u00f4ng c\u1ea7n ph\u1ea3i d\u00e0nh nhi\u1ec1u th\u1eddi gian v\u00e0 v\u1eabn c\u00f3 th\u1ec3 h\u1ecdc \u0111\u01b0\u1ee3c s\u1ed1 21 La M\u00e3 m\u1ed9t c\u00e1ch d\u1ec5 d\u00e0ng. Theo \u0111\u00f3, c\u00e1ch vi\u1ebft s\u1ed1 La M\u00e3 d\u1ef1a tr\u00ean c\u00e1c quy t\u1eafc sau:<\/p>\n<ul>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">X l\u00e0 10, c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c l\u1eb7p l\u1ea1i v\u00e0 trong s\u1ed1 21, x l\u1eb7p l\u1ea1i 2 l\u1ea7n, mang gi\u00e1 tr\u1ecb 20. Do \u0111\u00f3, ch\u1eef X v\u1eabn tu\u00e2n theo nguy\u00ean t\u1eafc kh\u00f4ng l\u1eb7p l\u1ea1i h\u01a1n ba l\u1ea7n.<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">T\u00f4i l\u00e0 1, \u0111\u01b0\u1ee3c th\u00eam v\u00e0o b\u00ean ph\u1ea3i c\u1ee7a XX &#8211; hai m\u01b0\u01a1i, IE \u0111\u00e3 th\u00eam.<\/p>\n<\/li>\n<\/ul>\n<h2 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Mot_so_loai_bai_tap_tren_so_21_o_Rome_la_pho_bien_trong_bai_kiem_tra\"><\/span>M\u1ed9t s\u1ed1 lo\u1ea1i b\u00e0i t\u1eadp tr\u00ean s\u1ed1 21 \u1edf Rome l\u00e0 ph\u1ed5 bi\u1ebfn trong b\u00e0i ki\u1ec3m tra<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p dir=\"ltr\">S\u1ed1 21 l\u00e0 m\u1ed9t m\u00e3 l\u00e0 m\u1ed9t s\u1ed1 quen thu\u1ed9c, v\u00ec v\u1eady trong c\u00e1c b\u00e0i ki\u1ec3m tra, n\u00f3 th\u01b0\u1eddng xu\u1ea5t hi\u1ec7n kh\u00e1 nhi\u1ec1u v\u1edbi c\u00e1c lo\u1ea1i b\u00e0i t\u1eadp kh\u00e1c nhau. D\u01b0\u1edbi \u0111\u00e2y l\u00e0 m\u1ed9t s\u1ed1 lo\u1ea1i b\u00e0i t\u1eadp ph\u1ed5 bi\u1ebfn nh\u1ea5t li\u00ean quan \u0111\u1ebfn s\u1ed1 n\u00e0y:<\/p>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Mau_1_Them_so_21_cua_La_Ma\"><\/span>M\u1eabu 1: Th\u00eam s\u1ed1 21 c\u1ee7a La M\u00e3<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">H\u00ecnh th\u1ee9c \u0111\u1ea7u ti\u00ean c\u1ee7a c\u00e1c b\u00e0i t\u1eadp m\u00e0 tr\u1ebb ph\u1ed5 bi\u1ebfn nh\u1ea5t trong c\u00e1c b\u00e0i t\u1eadp \u0111\u00f3 l\u00e0 th\u00eam 21 s\u1ed1 La M\u00e3. Khi b\u1ea1n mu\u1ed1n th\u1ef1c hi\u1ec7n bi\u1ec3u m\u1eabu n\u00e0y, b\u1ea1n s\u1ebd l\u00e0m theo ba b\u01b0\u1edbc sau:<\/p>\n<p dir=\"ltr\"><img decoding=\"async\" class=\"lazyload\" src=\"https:\/\/external-content.duckduckgo.com\/iu\/?u=https:\/\/vnmedia2.monkeyuni.net\/upload\/web\/img\/3-21-so-la-ma.jpg\" alt=\"Kh\u1ea5u tr\u1eeb h\u00e0nh \u0111\u1ed9ng s\u1ed1 21 La M\u00e3 (Ngu\u1ed3n: B\u1ed9 s\u01b0u t\u1eadp Internet)\" width=\"100%\"><\/p>\n<ul>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">B\u01b0\u1edbc 1: Tr\u1ebb em s\u1ebd \u0111\u1ecdc v\u1ea5n \u0111\u1ec1 v\u00e0 sau \u0111\u00f3 xem c\u00e1ch c\u00e1c nh\u00e2n v\u1eadt La M\u00e3 xu\u1ea5t hi\u1ec7n trong ch\u1ee7 \u0111\u1ec1 v\u00e0 chuy\u1ec3n ch\u00fang th\u00e0nh c\u00e1c s\u1ed1 t\u1ef1 nhi\u00ean \u0111\u1ec3 gi\u00fap d\u1ec5 d\u00e0ng th\u1ef1c hi\u1ec7n c\u00e1c t\u00ednh to\u00e1n.<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">B\u01b0\u1edbc 2: Ti\u1ebfp theo, tr\u1ebb em s\u1ebd th\u1ef1c hi\u1ec7n vi\u1ec7c b\u1ed5 sung v\u00e0 tr\u1eeb c\u00e1c s\u1ed1 t\u1ef1 nhi\u00ean v\u1eeba \u0111\u01b0\u1ee3c chuy\u1ec3n \u0111\u1ed5i.<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">B\u01b0\u1edbc 3: Khi k\u1ebft qu\u1ea3 c\u00f3, tr\u1ebb s\u1ebd chuy\u1ec3n \u0111\u1ed5i s\u1ed1 n\u00e0y th\u00e0nh s\u1ed1 La M\u00e3 v\u00e0 vi\u1ebft c\u00e2u tr\u1ea3 l\u1eddi cho b\u00e0i ki\u1ec3m tra.<\/p>\n<\/li>\n<\/ul>\n<p dir=\"ltr\">V\u00ed d\u1ee5 XX &#8211; VIII =?<\/p>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Mau_2_Xac_dinh_so_21_trong_chuoi_da_cho\"><\/span>M\u1eabu 2: X\u00e1c \u0111\u1ecbnh s\u1ed1 21 trong chu\u1ed7i \u0111\u00e3 cho<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">Lo\u1ea1i b\u00e0i t\u1eadp ti\u1ebfp theo r\u1ea5t ph\u1ed5 bi\u1ebfn trong c\u00e1c th\u1eed nghi\u1ec7m hi\u1ec7n t\u1ea1i \u0111ang x\u00e1c \u0111\u1ecbnh 21 s\u1ed1 La M\u00e3 trong chu\u1ed7i s\u1ed1 \u0111\u00e3 cho. Nh\u1eefng \u0111\u1ee9a tr\u1ebb mu\u1ed1n bi\u1ebft s\u1ed1 21 n\u00e0y ph\u1ea3i n\u1eafm b\u1eaft c\u00e1ch vi\u1ebft \u0111\u1ec3 ch\u00fang c\u00f3 th\u1ec3 d\u1ec5 d\u00e0ng \u0111\u01b0a ch\u00fang v\u00e0o b\u00e0i ki\u1ec3m tra.<\/p>\n<p dir=\"ltr\">V\u00ed d\u1ee5: T\u00ecm s\u1ed1 21 l\u00e0 m\u00e3 trong chu\u1ed7i sau: xxx, xxi, xxv, xxii, xxiii<\/p>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Mau_3_So_sanh_so_luong_Roman_voi_21\"><\/span>M\u1eabu 3: So s\u00e1nh s\u1ed1 l\u01b0\u1ee3ng Roman v\u1edbi 21<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">M\u1ed9t h\u00ecnh th\u1ee9c b\u00e0i t\u1eadp kh\u00e1c c\u0169ng kh\u00e1 ph\u1ed5 bi\u1ebfn trong c\u00e1c b\u00e0i ki\u1ec3m tra hi\u1ec7n t\u1ea1i l\u00e0 c\u00e1c b\u00e0i t\u1eadp so s\u00e1nh 21 s\u1ed1 v\u1edbi c\u00e1c s\u1ed1 kh\u00e1c.<\/p>\n<p dir=\"ltr\">\u0110\u00e2y l\u00e0 m\u1ed9t lo\u1ea1i b\u00e0i t\u1eadp kh\u00e1 kh\u00f3 kh\u0103n v\u00ec tr\u1ebb em c\u1ea7n x\u00e1c \u0111\u1ecbnh c\u00e1c nh\u00e2n v\u1eadt La M\u00e3 \u0111\u1ec3 c\u00f3 th\u1ec3 th\u1ef1c hi\u1ec7n so s\u00e1nh. Sau khi x\u00e1c \u0111\u1ecbnh ch\u00ednh x\u00e1c c\u00e1c s\u1ed1, tr\u1ebb s\u1ebd \u0111i\u1ec1n v\u00e0o con d\u1ea5u&gt;, &lt;, =. <\/p>\n<p dir=\"ltr\"><img decoding=\"async\" class=\"lazyload\" src=\"https:\/\/external-content.duckduckgo.com\/iu\/?u=https:\/\/vnmedia2.monkeyuni.net\/upload\/web\/img\/4-21-so-la-ma.jpg\" alt=\"So s\u00e1nh s\u1ed1 21 trong Rome (Ngu\u1ed3n h\u00ecnh \u1ea3nh: B\u1ed9 s\u01b0u t\u1eadp Internet)\" width=\"100%\"><\/p>\n<p dir=\"ltr\">V\u00ed d\u1ee5: So s\u00e1nh XXI v\u00e0 XXII<\/p>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Mau_4_Doc_va_viet_so_binh_thuong_cho_banh_rang_La_Ma_va_nguoc_lai_21\"><\/span>M\u1eabu 4: \u0110\u1ecdc v\u00e0 vi\u1ebft s\u1ed1 b\u00ecnh th\u01b0\u1eddng cho b\u00e1nh r\u0103ng La M\u00e3 v\u00e0 ng\u01b0\u1ee3c l\u1ea1i 21<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">\u0110\u00f3 l\u00e0 m\u1ed9t h\u00ecnh th\u1ee9c b\u00e0i t\u1eadp c\u01a1 b\u1ea3n m\u00e0 h\u1ea7u h\u1ebft tr\u1ebb em s\u1ebd \u0111\u01b0\u1ee3c th\u1ef1c h\u00e0nh b\u1edfi gi\u00e1o vi\u00ean v\u00e0 ph\u1ee5 huynh. Theo \u0111\u00f3, ch\u1ee7 \u0111\u1ec1 s\u1ebd y\u00eau c\u1ea7u tr\u1ebb \u0111\u1ecdc v\u00e0 vi\u1ebft s\u1ed1 21 La M\u00e3 t\u1eeb c\u00e1c s\u1ed1 th\u00f4ng th\u01b0\u1eddng.<\/p>\n<p dir=\"ltr\">\u0110\u1ec3 c\u00f3 th\u1ec3 th\u1ef1c hi\u1ec7n b\u00e0i t\u1eadp n\u00e0y, b\u1ea1n ch\u1ec9 c\u1ea7n nh\u1edb c\u00e1c quy t\u1eafc \u0111\u1ecdc c\u0169ng nh\u01b0 c\u00e1c quy t\u1eafc vi\u1ebft c\u1ee7a s\u1ed1 21. Khi b\u1ea1n nh\u1edb c\u00e1c quy t\u1eafc \u0111\u1ecdc v\u00e0 vi\u1ebft, tr\u1ebb em c\u00f3 th\u1ec3 th\u1ef1c hi\u1ec7n b\u00e0i t\u1eadp n\u00e0y r\u1ea5t \u0111\u01a1n gi\u1ea3n. <\/p>\n<p dir=\"ltr\">V\u00ed d\u1ee5: \u0110\u1ecdc v\u00e0 vi\u1ebft s\u1ed1 21 Roman.<\/p>\n<h2 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"De_xuat_mot_so_bai_tap_ve_21_so_La_Ma_de_giup_tre_thuc_hanh_hieu_qua\"><\/span>\u0110\u1ec1 xu\u1ea5t m\u1ed9t s\u1ed1 b\u00e0i t\u1eadp v\u1ec1 21 s\u1ed1 La M\u00e3 \u0111\u1ec3 gi\u00fap tr\u1ebb th\u1ef1c h\u00e0nh hi\u1ec7u qu\u1ea3<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p dir=\"ltr\">N\u1ebfu cha m\u1eb9 v\u1eabn kh\u00f4ng bi\u1ebft l\u1ef1a ch\u1ecdn b\u00e0i t\u1eadp n\u00e0o cho con c\u00e1i h\u1ecd th\u1ef1c h\u00e0nh trong k\u1ef3 ngh\u1ec9 h\u00e8 n\u00e0y, cha m\u1eb9 n\u00ean ngay l\u1eadp t\u1ee9c tham kh\u1ea3o c\u00e1c b\u00e0i t\u1eadp sau:<\/p>\n<p dir=\"ltr\"><img decoding=\"async\" class=\"lazyload\" src=\"https:\/\/external-content.duckduckgo.com\/iu\/?u=https:\/\/vnmedia2.monkeyuni.net\/upload\/web\/img\/5-21-so-la-ma.jpg\" alt=\"C\u00e1c b\u00e0i t\u1eadp li\u00ean quan \u0111\u1ebfn 21 La M\u00e3 (Ngu\u1ed3n: B\u1ed9 s\u01b0u t\u1eadp Internet)\" width=\"100%\"><\/p>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Bai_tap_1\"><\/span>B\u00e0i t\u1eadp 1<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">\u0110\u1ecdc v\u00e0 vi\u1ebft 21 s\u1ed1 La M\u00e3.<\/p>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Bai_tap_2\"><\/span>B\u00e0i t\u1eadp 2 <span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">\u0110i\u1ec1n v\u00e0o con d\u1ea5u&gt;, &lt;, = trong c\u00e1c tr\u01b0\u1eddng h\u1ee3p sau:<\/p>\n<ol>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">XXI &#8230; XIX<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">Xxix &#8230; xxi<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">Xviii &#8230; xxi<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">Xxi &#8230; viii<\/p>\n<\/li>\n<\/ol>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Bai_tap_3\"><\/span>B\u00e0i t\u1eadp 3 <span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">T\u00ecm s\u1ed1 21 v\u00e0 v\u00f2ng tr\u00f2n theo tr\u00ecnh t\u1ef1 sau: XXVIII, XXI, XIX, XXIX, XXIII<\/p>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Bai_tap_4\"><\/span>B\u00e0i t\u1eadp 4 <span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">Th\u1ef1c hi\u1ec7n c\u00e1c t\u00ednh to\u00e1n sau:<\/p>\n<ol>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">Xxi + xxvi<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">Xxix + xxi<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">XXI + VIII<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">XXI + IX<\/p>\n<\/li>\n<\/ol>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Bai_tap_5\"><\/span>B\u00e0i t\u1eadp 5 <span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">Th\u1ef1c hi\u1ec7n c\u00e1c t\u00ednh to\u00e1n sau:<\/p>\n<ol>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">XXI &#8211; IX<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">Xxx &#8211; xxi<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">XXI &#8211; VIII<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">XC &#8211; XXI<\/p>\n<\/li>\n<\/ol>\n<h3 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Bai_tap_6\"><\/span>B\u00e0i t\u1eadp 6<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\">Th\u1ef1c hi\u1ec7n c\u00e1c t\u00ednh to\u00e1n sau:<\/p>\n<ol>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">Xxi + xxx<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">Xxi &#8211; v<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">C &#8211; XXI<\/p>\n<\/li>\n<li dir=\"ltr\">\n<p dir=\"ltr\" role=\"presentation\">M + xxi<\/p>\n<\/li>\n<\/ol>\n<p>Xem th\u00eam: H\u01b0\u1edbng d\u1eabn v\u1ec1 c\u00e1ch \u0111\u1ecdc v\u00e0 vi\u1ebft s\u1ed1 La M\u00e3 ti\u00eau chu\u1ea9n 2007 kh\u00f4ng ph\u1ea3i ai c\u0169ng bi\u1ebft<\/p>\n<h2 dir=\"ltr\"><span class=\"ez-toc-section\" id=\"Bi_quyet_de_giup_em_be_cua_ban_nho_so_21_cua_nguoi_La_Ma_don_gian\"><\/span>B\u00ed quy\u1ebft \u0111\u1ec3 gi\u00fap em b\u00e9 c\u1ee7a b\u1ea1n nh\u1edb s\u1ed1 21 c\u1ee7a ng\u01b0\u1eddi La M\u00e3 \u0111\u01a1n gi\u1ea3n<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p dir=\"ltr\">21 S\u1ed1 La M\u00e3 kh\u00f4ng qu\u00e1 kh\u00f3 \u0111\u1ec3 l\u00e0m quen. Nh\u01b0ng n\u1ebfu kh\u00f4ng c\u00f3 ph\u01b0\u01a1ng ph\u00e1p gi\u1ea3ng d\u1ea1y th\u00edch h\u1ee3p, tr\u1ebb s\u1ebd kh\u00f3 l\u00e0m quen v\u1edbi con s\u1ed1 n\u00e0y.<\/p>\n<p dir=\"ltr\">Do \u0111\u00f3, \u0111\u00e2y l\u00e0 m\u1ed9t s\u1ed1 ph\u01b0\u01a1ng ph\u00e1p m\u00e0 cha m\u1eb9 c\u1ea7n b\u1ecf t\u00fai \u0111\u1ec3 gi\u00fap con c\u00e1i h\u1ecd h\u1ecdc t\u1ed1t s\u1ed1 21 Roman:<\/p>\n<p dir=\"ltr\"><img decoding=\"async\" class=\"lazyload\" src=\"https:\/\/external-content.duckduckgo.com\/iu\/?u=https:\/\/vnmedia2.monkeyuni.net\/upload\/web\/img\/6-21-so-la-ma.jpg\" alt=\"L\u00e0m th\u1ebf n\u00e0o \u0111\u1ec3 gi\u00fap tr\u1ebb h\u1ecdc \u0111\u01b0\u1ee3c s\u1ed1 21 La M\u00e3? (Ngu\u1ed3n h\u00ecnh \u1ea3nh: B\u1ed9 s\u01b0u t\u1eadp Internet)\" width=\"100%\"><\/p>\n<h3 dir=\"ltr\" role=\"presentation\"><span class=\"ez-toc-section\" id=\"Hay_nho_quy_tac_viet_21_Roman\"><\/span>H\u00e3y nh\u1edb quy t\u1eafc vi\u1ebft 21 Roman<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\" role=\"presentation\">N\u1ebfu \u0111\u1ee9a tr\u1ebb h\u1ecdc t\u1ed1t, ng\u01b0\u1eddi La M\u00e3 21, cha m\u1eb9 c\u1ea7n gi\u00fap con m\u00ecnh nh\u1edb v\u1ec1 quy t\u1eafc vi\u1ebft s\u1ed1 n\u00e0y. Khi con b\u1ea1n \u0111\u00e3 ghi nh\u1edb quy t\u1eafc vi\u1ebft, tr\u1ebb em c\u00f3 th\u1ec3 t\u1ef1 tin th\u1ef1c hi\u1ec7n t\u1ea5t c\u1ea3 c\u00e1c b\u00e0i t\u1eadp li\u00ean quan \u0111\u1ebfn Roman s\u1ed1 21.<\/p>\n<h3 dir=\"ltr\" role=\"presentation\"><span class=\"ez-toc-section\" id=\"Thuc_hanh_thuong_xuyen_voi_21\"><\/span>Th\u1ef1c h\u00e0nh th\u01b0\u1eddng xuy\u00ean v\u1edbi 21<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\" role=\"presentation\">B\u00ed quy\u1ebft th\u1ee9 hai \u0111\u1ec3 gi\u00fap tr\u1ebb em c\u00f3 th\u1ec3 nh\u1edb s\u1ed1 21 \u0111\u00f3 l\u00e0 cha m\u1eb9 cho con c\u00e1i h\u1ecd th\u1ef1c h\u00e0nh th\u01b0\u1eddng xuy\u00ean v\u1edbi con s\u1ed1 n\u00e0y.<\/p>\n<p dir=\"ltr\" role=\"presentation\">Ch\u1ec9 khi tr\u1ebb th\u1ef1c hi\u1ec7n c\u00e1c b\u00e0i t\u1eadp r\u1ea5t nhi\u1ec1u, h\u00e3y th\u1ef1c h\u00e0nh c\u00e1c b\u00e0i t\u1eadp v\u1edbi s\u1ed1 21 La M\u00e3, tr\u1ebb em s\u1ebd kh\u00f4ng ng\u1ea1c nhi\u00ean khi g\u1eb7p c\u00e1c b\u00e0i t\u1eadp li\u00ean quan \u0111\u1ebfn s\u1ed1 21 trong b\u00e0i ki\u1ec3m tra.<\/p>\n<h3 dir=\"ltr\" role=\"presentation\"><span class=\"ez-toc-section\" id=\"Choi_tro_choi_voi_21_nguoi_La_Ma\"><\/span>Ch\u01a1i tr\u00f2 ch\u01a1i v\u1edbi 21 ng\u01b0\u1eddi La M\u00e3<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\" role=\"presentation\">Tr\u1ebb nh\u1ecf th\u00edch tham gia v\u00e0o c\u00e1c tr\u00f2 ch\u01a1i. Do \u0111\u00f3, n\u1ebfu cha m\u1eb9 mu\u1ed1n con c\u00e1i c\u1ee7a h\u1ecd h\u1ecdc t\u1ed1t s\u1ed1 21 La M\u00e3, cha m\u1eb9 n\u00ean t\u00edch h\u1ee3p s\u1ef1 xu\u1ea5t hi\u1ec7n c\u1ee7a 21 trong c\u00e1c tr\u00f2 ch\u01a1i.<\/p>\n<p dir=\"ltr\" role=\"presentation\">T\u00e2m l\u00fd c\u1ee7a em b\u00e9 khi tham gia v\u00e0o c\u00e1c tr\u00f2 ch\u01a1i v\u00e0 v\u1eabn h\u1ecdc ki\u1ebfn \u200b\u200bth\u1ee9c s\u1ebd c\u1ef1c k\u1ef3 tho\u1ea3i m\u00e1i. Khi tr\u1ebb kh\u00f4ng ch\u1ecbu \u00e1p l\u1ef1c, tr\u1ebb em c\u00f3 th\u1ec3 ti\u1ebfp c\u1eadn 21 s\u1ed1 La M\u00e3 d\u1ec5 d\u00e0ng h\u01a1n.<\/p>\n<h3 dir=\"ltr\" role=\"presentation\"><span class=\"ez-toc-section\" id=\"Phan_biet_cac_ky_tu_de_tranh_su_nham_lan\"><\/span>Ph\u00e2n bi\u1ec7t c\u00e1c k\u00fd t\u1ef1 \u0111\u1ec3 tr\u00e1nh s\u1ef1 nh\u1ea7m l\u1eabn<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\" role=\"presentation\">Quy t\u1eafc vi\u1ebft v\u00e0 \u0111\u1ecdc s\u1ed1 21 r\u1ea5t \u0111\u01a1n gi\u1ea3n v\u00e0 c\u00f3 nhi\u1ec1u r\u1eafc r\u1ed1i, v\u00ec v\u1eady kh\u00f4ng qu\u00e1 kh\u00f3 \u0111\u1ec3 ph\u00e2n bi\u1ec7t c\u00e1c k\u00fd t\u1ef1. Nh\u1eefng \u0111\u1ee9a tr\u1ebb ch\u1ec9 c\u1ea7n n\u1eafm b\u1eaft quy t\u1eafc vi\u1ebft \u0111\u1ec3 c\u00f3 th\u1ec3 ph\u00e2n bi\u1ec7t c\u00e1c nh\u00e2n v\u1eadt xu\u1ea5t hi\u1ec7n trong s\u1ed1 21 n\u00e0y.<\/p>\n<h3 dir=\"ltr\" role=\"presentation\"><span class=\"ez-toc-section\" id=\"Thuc_hanh_viet_va_dat_cau_hoi_ve_so_La_Ma_21\"><\/span>Th\u1ef1c h\u00e0nh vi\u1ebft v\u00e0 \u0111\u1eb7t c\u00e2u h\u1ecfi v\u1ec1 s\u1ed1 La M\u00e3 21<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p dir=\"ltr\" role=\"presentation\">\u0110\u1ec3 k\u00edch th\u00edch s\u1ef1 s\u00e1ng t\u1ea1o c\u1ee7a em b\u00e9, cha m\u1eb9 n\u00ean th\u1ef1c h\u00e0nh v\u00e0 \u0111\u1eb7t c\u00e2u h\u1ecfi li\u00ean quan \u0111\u1ebfn s\u1ed1 ng\u01b0\u1eddi La M\u00e3 21. Khi em b\u00e9 \u0111\u1eb7t c\u00e2u h\u1ecfi li\u00ean quan \u0111\u1ebfn con s\u1ed1 n\u00e0y, tr\u1ebb s\u1ebd hi\u1ec3u b\u1ea3n ch\u1ea5t c\u1ee7a 21 s\u1ed1 La M\u00e3 v\u00e0 th\u1ef1c hi\u1ec7n c\u00e1c b\u00e0i t\u1eadp d\u1ec5 d\u00e0ng h\u01a1n.<\/p>\n<\/p>\n<p dir=\"ltr\">B\u00e2y gi\u1edd tr\u1ebb em bi\u1ebft 21 s\u1ed1 La M\u00e3 \u0111\u00e3 \u0111\u1ecdc v\u00e0 l\u00e0m th\u1ebf n\u00e0o \u0111\u1ec3 vi\u1ebft hay kh\u00f4ng? Con s\u1ed1 n\u00e0y kh\u00f4ng qu\u00e1 kh\u00f3, v\u00ec v\u1eady n\u1ebfu b\u1ea1n mu\u1ed1n h\u1ecdc v\u00e0 vi\u1ebft, b\u1ea1n ch\u1ec9 c\u1ea7n l\u01b0u \u00fd m\u1ed9t v\u1ea5n \u0111\u1ec1 c\u00f3 th\u1ec3 nh\u1edb s\u1ed1 21 trong 5 ph\u00fat.<\/p>\n<p>                                    Ngu\u1ed3n tham chi\u1ebfu<\/p>\n<p>21 trong S\u1ed1 La M\u00e3 &#8211; Truy c\u1eadp ng\u00e0y 13 th\u00e1ng 7 n\u0103m 2022<\/p>\n<p>https:\/\/byjus.com\/maths\/21-in-roman-numerals\/#:~: Text = 21%20in%20Roman%20Numerals%20is%20xXi.<\/p>\n<p>21 trong S\u1ed1 La M\u00e3 &#8211; Truy c\u1eadp ng\u00e0y 13 th\u00e1ng 7 n\u0103m 2022<\/p>\n<p>https:\/\/www.cuemath.com\/numbers\/21-in-roman-numerals\/<\/p>\n<p>Ngu\u1ed3n: <a href=\"http:\/\/www.ckconitsha.com\/vn\/\">http:\/\/www.ckconitsha.com\/vn\/<\/a> T\u00e1c gi\u1ea3: <a href=\"https:\/\/www.ckconitsha.com\/vn\/author\/nguyenlandung\">Nguy\u1ec5n L\u00e2n d\u0169ng<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>L\u00e0m th\u1ebf n\u00e0o \u0111\u1ec3 \u0111\u1ecdc v\u00e0 vi\u1ebft 21 s\u1ed1 La M\u00e3 c\u00f3 v\u1ebb \u0111\u01a1n gi\u1ea3n, nh\u01b0ng nhi\u1ec1u tr\u1ebb em khi l\u00e0m b\u00e0i t\u1eadp v\u1ec1 nh\u00e0 r\u1ea5t d\u1ec5 nh\u1ea7m l\u1eabn v\u00e0 l\u00e0m sai. V\u00ec v\u1eady, b\u00e0i vi\u1ebft sau \u0111\u00e2y s\u1ebd h\u01b0\u1edbng d\u1eabn c\u00e1ch em b\u00e9 c\u1ee7a b\u1ea1n bi\u1ebft c\u00e1ch \u0111\u1ecdc, vi\u1ebft v\u00e0 l\u00e0m b\u00e0i t\u1eadp v\u1ec1&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[100],"tags":[],"class_list":["post-19183","post","type-post","status-publish","format-standard","hentry","category-kien-thuc"],"_links":{"self":[{"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/posts\/19183","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/comments?post=19183"}],"version-history":[{"count":2,"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/posts\/19183\/revisions"}],"predecessor-version":[{"id":25004,"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/posts\/19183\/revisions\/25004"}],"wp:attachment":[{"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/media?parent=19183"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/categories?post=19183"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ckconitsha.com\/vn\/wp-json\/wp\/v2\/tags?post=19183"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}