{"id":570073,"date":"2026-07-24T12:50:17","date_gmt":"2026-07-24T05:50:17","guid":{"rendered":"https:\/\/hoanghamobile.com\/tin-tuc\/?p=570073"},"modified":"2026-08-25T16:12:52","modified_gmt":"2026-08-25T09:12:52","slug":"can-bac-hai-la-gi","status":"publish","type":"post","link":"https:\/\/hoanghamobile.com\/tin-tuc\/can-bac-hai-la-gi\/","title":{"rendered":"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c v\u00e0 b\u00e0i t\u1eadp"},"content":{"rendered":"<p><strong>C\u0103n b\u1eadc hai c\u1ee7a m\u1ed9t s\u1ed1 a kh\u00f4ng \u00e2m l\u00e0 s\u1ed1 x sao cho x\u00b2 = a; trong \u0111\u00f3 c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc c\u1ee7a a l\u00e0 s\u1ed1 kh\u00f4ng \u00e2m, k\u00fd hi\u1ec7u l\u00e0 \u221aa.<\/strong> V\u00ed d\u1ee5, c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc c\u1ee7a 25 l\u00e0 5 v\u00ec 5\u00b2 = 25. \u0110\u00e2y l\u00e0 ki\u1ebfn th\u1ee9c n\u1ec1n t\u1ea3ng c\u1ee7a To\u00e1n l\u1edbp 7 v\u00e0 l\u1edbp 9, xu\u1ea5t hi\u1ec7n th\u01b0\u1eddng xuy\u00ean trong h\u00ecnh h\u1ecdc v\u00e0 \u0111\u1ea1i s\u1ed1. B\u00e0i vi\u1ebft n\u00e0y tr\u00ecnh b\u00e0y c\u0103n b\u1eadc hai l\u00e0 g\u00ec, c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00e1c t\u00ednh ch\u1ea5t, b\u1ea3ng c\u0103n b\u1eadc hai th\u01b0\u1eddng g\u1eb7p, c\u00e1ch t\u00ednh v\u00e0 nhi\u1ec1u b\u00e0i t\u1eadp v\u1eadn d\u1ee5ng c\u00f3 l\u1eddi gi\u1ea3i chi ti\u1ebft \u0111\u1ec3 b\u1ea1n n\u1eafm ch\u1eafc ki\u1ebfn th\u1ee9c.<\/p>\n<h2>C\u0103n b\u1eadc hai l\u00e0 g\u00ec?<\/h2>\n<p>C\u0103n b\u1eadc hai c\u1ee7a m\u1ed9t s\u1ed1 a kh\u00f4ng \u00e2m l\u00e0 s\u1ed1 x sao cho x\u00b2 = a. V\u1edbi m\u1ed7i s\u1ed1 d\u01b0\u01a1ng a, lu\u00f4n c\u00f3 <strong>hai c\u0103n b\u1eadc hai<\/strong> l\u00e0 hai s\u1ed1 \u0111\u1ed1i nhau: m\u1ed9t s\u1ed1 d\u01b0\u01a1ng \u221aa v\u00e0 m\u1ed9t s\u1ed1 \u00e2m \u2212\u221aa. V\u00ed d\u1ee5, s\u1ed1 9 c\u00f3 hai c\u0103n b\u1eadc hai l\u00e0 3 v\u00e0 \u22123, v\u00ec 3\u00b2 = 9 v\u00e0 (\u22123)\u00b2 = 9. Ri\u00eang s\u1ed1 0 ch\u1ec9 c\u00f3 m\u1ed9t c\u0103n b\u1eadc hai l\u00e0 0, c\u00f2n s\u1ed1 \u00e2m kh\u00f4ng c\u00f3 c\u0103n b\u1eadc hai trong t\u1eadp s\u1ed1 th\u1ef1c v\u00ec b\u00ecnh ph\u01b0\u01a1ng c\u1ee7a m\u1ecdi s\u1ed1 th\u1ef1c \u0111\u1ec1u kh\u00f4ng \u00e2m.<\/p>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"aligncenter size-full wp-image-570076\" src=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-1.jpg\" alt=\"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c v\u00e0 b\u00e0i t\u1eadp - c\u0103n b\u1eadc hai l\u00e0 g\u00ec\" width=\"800\" height=\"450\" srcset=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-1.jpg 800w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-1-300x169.jpg 300w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-1-768x432.jpg 768w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><\/p>\n<h2>C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc<\/h2>\n<p>C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc c\u1ee7a m\u1ed9t s\u1ed1 a kh\u00f4ng \u00e2m l\u00e0 <strong>c\u0103n b\u1eadc hai kh\u00f4ng \u00e2m<\/strong> c\u1ee7a a, k\u00fd hi\u1ec7u l\u00e0 \u221aa. V\u00ed d\u1ee5: \u221a25 = 5 (kh\u00f4ng ph\u1ea3i \u22125), \u221a16 = 4, \u221a0 = 0. Khi n\u00f3i &#8220;c\u0103n b\u1eadc hai&#8221; trong c\u00e1c b\u00e0i to\u00e1n th\u00f4ng th\u01b0\u1eddng, ta th\u01b0\u1eddng hi\u1ec3u l\u00e0 c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc. C\u1ea7n ph\u00e2n bi\u1ec7t r\u00f5: &#8220;c\u00e1c c\u0103n b\u1eadc hai c\u1ee7a 25&#8221; g\u1ed3m c\u1ea3 5 v\u00e0 \u22125, c\u00f2n &#8220;c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc c\u1ee7a 25&#8221; ch\u1ec9 l\u00e0 5.<\/p>\n<h2>\u0110i\u1ec1u ki\u1ec7n x\u00e1c \u0111\u1ecbnh v\u00e0 k\u00fd hi\u1ec7u<\/h2>\n<p>Bi\u1ec3u th\u1ee9c \u221aA ch\u1ec9 c\u00f3 ngh\u0129a (x\u00e1c \u0111\u1ecbnh) khi <strong>A \u2265 0<\/strong>. \u0110\u00e2y l\u00e0 \u0111i\u1ec1u ki\u1ec7n quan tr\u1ecdng khi gi\u1ea3i c\u00e1c b\u00e0i to\u00e1n t\u00ecm \u0111i\u1ec1u ki\u1ec7n x\u00e1c \u0111\u1ecbnh c\u1ee7a bi\u1ec3u th\u1ee9c ch\u1ee9a c\u0103n. V\u00ed d\u1ee5, \u221a(x \u2212 2) x\u00e1c \u0111\u1ecbnh khi x \u2212 2 \u2265 0, t\u1ee9c l\u00e0 x \u2265 2. D\u1ea5u c\u0103n &#8220;\u221a&#8221; c\u00f2n g\u1ecdi l\u00e0 d\u1ea5u c\u0103n th\u1ee9c b\u1eadc hai, bi\u1ec3u th\u1ee9c n\u1eb1m d\u01b0\u1edbi d\u1ea5u c\u0103n g\u1ecdi l\u00e0 bi\u1ec3u th\u1ee9c d\u01b0\u1edbi d\u1ea5u c\u0103n.<\/p>\n<h2>C\u00e1c t\u00ednh ch\u1ea5t v\u00e0 c\u00f4ng th\u1ee9c v\u1ec1 c\u0103n b\u1eadc hai<\/h2>\n<p>D\u01b0\u1edbi \u0111\u00e2y l\u00e0 c\u00e1c c\u00f4ng th\u1ee9c c\u01a1 b\u1ea3n th\u01b0\u1eddng d\u00f9ng khi bi\u1ebfn \u0111\u1ed5i v\u00e0 r\u00fat g\u1ecdn bi\u1ec3u th\u1ee9c ch\u1ee9a c\u0103n b\u1eadc hai.<\/p>\n<table>\n<thead>\n<tr>\n<th>C\u00f4ng th\u1ee9c<\/th>\n<th>\u0110i\u1ec1u ki\u1ec7n<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>\u221a(a\u00b2) = |a|<\/td>\n<td>V\u1edbi m\u1ecdi s\u1ed1 a<\/td>\n<\/tr>\n<tr>\n<td>\u221a(a \u00b7 b) = \u221aa \u00b7 \u221ab<\/td>\n<td>a \u2265 0, b \u2265 0<\/td>\n<\/tr>\n<tr>\n<td>\u221a(a\/b) = \u221aa \/ \u221ab<\/td>\n<td>a \u2265 0, b &gt; 0<\/td>\n<\/tr>\n<tr>\n<td>(\u221aa)\u00b2 = a<\/td>\n<td>a \u2265 0<\/td>\n<\/tr>\n<tr>\n<td>\u221aa &lt; \u221ab \u21d4 a &lt; b<\/td>\n<td>a \u2265 0, b \u2265 0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>L\u01b0u \u00fd quan tr\u1ecdng: \u221a(a\u00b2) = |a| ch\u1ee9 kh\u00f4ng ph\u1ea3i lu\u00f4n b\u1eb1ng a; v\u00ed d\u1ee5 \u221a((\u22123)\u00b2) = |\u22123| = 3. Ngo\u00e0i ra, c\u0103n b\u1eadc hai b\u1ea3o to\u00e0n th\u1ee9 t\u1ef1: s\u1ed1 n\u00e0o l\u1edbn h\u01a1n th\u00ec c\u00f3 c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc l\u1edbn h\u01a1n, nh\u1edd \u0111\u00f3 ta c\u00f3 th\u1ec3 so s\u00e1nh c\u00e1c c\u0103n m\u00e0 kh\u00f4ng c\u1ea7n t\u00ednh gi\u00e1 tr\u1ecb g\u1ea7n \u0111\u00fang.<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-570077\" src=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-2.jpg\" alt=\"C\u00e1c t\u00ednh ch\u1ea5t v\u00e0 c\u00f4ng th\u1ee9c v\u1ec1 c\u0103n b\u1eadc hai\" width=\"800\" height=\"450\" srcset=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-2.jpg 800w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-2-300x169.jpg 300w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-2-768x432.jpg 768w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><\/p>\n<h2>B\u1ea3ng c\u0103n b\u1eadc hai c\u1ee7a m\u1ed9t s\u1ed1 s\u1ed1 ch\u00ednh ph\u01b0\u01a1ng<\/h2>\n<p>Ghi nh\u1edb c\u0103n b\u1eadc hai c\u1ee7a c\u00e1c s\u1ed1 ch\u00ednh ph\u01b0\u01a1ng gi\u00fap t\u00ednh to\u00e1n nhanh h\u01a1n: \u221a1 = 1; \u221a4 = 2; \u221a9 = 3; \u221a16 = 4; \u221a25 = 5; \u221a36 = 6; \u221a49 = 7; \u221a64 = 8; \u221a81 = 9; \u221a100 = 10; \u221a121 = 11; \u221a144 = 12; \u221a169 = 13; \u221a196 = 14; \u221a225 = 15.<\/p>\n<h2>C\u00e1ch t\u00ednh c\u0103n b\u1eadc hai<\/h2>\n<p>V\u1edbi c\u00e1c s\u1ed1 ch\u00ednh ph\u01b0\u01a1ng, ta t\u00ednh tr\u1ef1c ti\u1ebfp d\u1ef1a v\u00e0o b\u1ea3ng tr\u00ean. V\u1edbi s\u1ed1 kh\u00f4ng ph\u1ea3i ch\u00ednh ph\u01b0\u01a1ng, k\u1ebft qu\u1ea3 l\u00e0 s\u1ed1 v\u00f4 t\u1ec9 v\u00e0 th\u01b0\u1eddng \u0111\u01b0\u1ee3c t\u00ednh g\u1ea7n \u0111\u00fang b\u1eb1ng m\u00e1y t\u00ednh b\u1ecf t\u00fai, v\u00ed d\u1ee5 \u221a2 \u2248 1,414; \u221a3 \u2248 1,732; \u221a5 \u2248 2,236. Ngo\u00e0i ra, c\u00f3 th\u1ec3 ph\u00e2n t\u00edch s\u1ed1 d\u01b0\u1edbi d\u1ea5u c\u0103n th\u00e0nh t\u00edch c\u1ee7a m\u1ed9t s\u1ed1 ch\u00ednh ph\u01b0\u01a1ng v\u1edbi s\u1ed1 c\u00f2n l\u1ea1i \u0111\u1ec3 r\u00fat g\u1ecdn, v\u00ed d\u1ee5 \u221a50 = \u221a(25 \u00d7 2) = 5\u221a2.<\/p>\n<h3>V\u00ed d\u1ee5 t\u00ednh c\u0103n b\u1eadc hai c\u00f3 l\u1eddi gi\u1ea3i t\u1eebng b\u01b0\u1edbc<\/h3>\n<p><strong>V\u00ed d\u1ee5:<\/strong> R\u00fat g\u1ecdn bi\u1ec3u th\u1ee9c \u221a48 + \u221a75 \u2212 \u221a12.<\/p>\n<ul>\n<li><strong>B\u01b0\u1edbc 1<\/strong> \u2014 Ph\u00e2n t\u00edch m\u1ed7i s\u1ed1 th\u00e0nh t\u00edch c\u1ee7a s\u1ed1 ch\u00ednh ph\u01b0\u01a1ng v\u1edbi s\u1ed1 c\u00f2n l\u1ea1i: 48 = 16 \u00d7 3; 75 = 25 \u00d7 3; 12 = 4 \u00d7 3.<\/li>\n<li><strong>B\u01b0\u1edbc 2<\/strong> \u2014 \u0110\u01b0a th\u1eeba s\u1ed1 ra ngo\u00e0i d\u1ea5u c\u0103n: \u221a48 = 4\u221a3; \u221a75 = 5\u221a3; \u221a12 = 2\u221a3.<\/li>\n<li><strong>B\u01b0\u1edbc 3<\/strong> \u2014 Thay l\u1ea1i v\u00e0o bi\u1ec3u th\u1ee9c: 4\u221a3 + 5\u221a3 \u2212 2\u221a3.<\/li>\n<li><strong>B\u01b0\u1edbc 4<\/strong> \u2014 C\u1ed9ng tr\u1eeb c\u00e1c c\u0103n \u0111\u1ed3ng d\u1ea1ng: (4 + 5 \u2212 2)\u221a3 = 7\u221a3.<\/li>\n<li><strong>K\u1ebft lu\u1eadn:<\/strong> \u221a48 + \u221a75 \u2212 \u221a12 = 7\u221a3.<\/li>\n<\/ul>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-570078\" src=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-3.jpg\" alt=\"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c v\u00e0 b\u00e0i t\u1eadp - v\u00ed d\u1ee5 t\u00ednh c\u0103n b\u1eadc hai c\u00f3 l\u1eddi gi\u1ea3i t\u1eebng b\u01b0\u1edbc\" width=\"800\" height=\"450\" srcset=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-3.jpg 800w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-3-300x169.jpg 300w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-3-768x432.jpg 768w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><\/p>\n<h2>B\u00e0i t\u1eadp v\u1eadn d\u1ee5ng c\u00f3 l\u1eddi gi\u1ea3i<\/h2>\n<ul>\n<li><strong>B\u00e0i 1:<\/strong> T\u00ednh \u221a64 v\u00e0 \u221a121. <em>L\u1eddi gi\u1ea3i:<\/em> \u221a64 = 8; \u221a121 = 11.<\/li>\n<li><strong>B\u00e0i 2:<\/strong> T\u00ecm t\u1ea5t c\u1ea3 c\u00e1c c\u0103n b\u1eadc hai c\u1ee7a 49. <em>L\u1eddi gi\u1ea3i:<\/em> c\u00f3 hai c\u0103n b\u1eadc hai l\u00e0 7 v\u00e0 \u22127.<\/li>\n<li><strong>B\u00e0i 3:<\/strong> R\u00fat g\u1ecdn \u221a72. <em>L\u1eddi gi\u1ea3i:<\/em> \u221a72 = \u221a(36 \u00d7 2) = 6\u221a2.<\/li>\n<li><strong>B\u00e0i 4:<\/strong> T\u00ednh \u221a((\u22125)\u00b2). <em>L\u1eddi gi\u1ea3i:<\/em> = |\u22125| = 5.<\/li>\n<li><strong>B\u00e0i 5:<\/strong> T\u00ecm \u0111i\u1ec1u ki\u1ec7n x\u00e1c \u0111\u1ecbnh c\u1ee7a \u221a(2x \u2212 6). <em>L\u1eddi gi\u1ea3i:<\/em> c\u0103n x\u00e1c \u0111\u1ecbnh khi 2x \u2212 6 \u2265 0 \u21d4 2x \u2265 6 \u21d4 x \u2265 3. V\u1eady \u0111i\u1ec1u ki\u1ec7n l\u00e0 x \u2265 3.<\/li>\n<li><strong>B\u00e0i 6:<\/strong> So s\u00e1nh \u221a17 v\u00e0 4. <em>L\u1eddi gi\u1ea3i:<\/em> vi\u1ebft 4 = \u221a16; v\u00ec 17 &gt; 16 n\u00ean \u221a17 &gt; \u221a16 = 4. V\u1eady \u221a17 &gt; 4.<\/li>\n<li><strong>B\u00e0i 7 (tr\u1eafc nghi\u1ec7m):<\/strong> C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc c\u1ee7a 81 l\u00e0 bao nhi\u00eau? A. \u22129 B. 9 C. C\u1ea3 9 v\u00e0 \u22129 D. 40,5. <em>\u0110\u00e1p \u00e1n:<\/em> B.<\/li>\n<\/ul>\n<h2>Ph\u00e2n bi\u1ec7t c\u0103n b\u1eadc hai v\u00e0 c\u0103n b\u1eadc ba<\/h2>\n<p>Nhi\u1ec1u b\u1ea1n d\u1ec5 nh\u1ea7m hai kh\u00e1i ni\u1ec7m n\u00e0y. C\u0103n b\u1eadc hai ch\u1ec9 x\u00e1c \u0111\u1ecbnh v\u1edbi s\u1ed1 kh\u00f4ng \u00e2m v\u00e0 s\u1ed1 d\u01b0\u01a1ng c\u00f3 t\u1edbi hai c\u0103n b\u1eadc hai. Ng\u01b0\u1ee3c l\u1ea1i, c\u0103n b\u1eadc ba (k\u00fd hi\u1ec7u \u221ba) x\u00e1c \u0111\u1ecbnh v\u1edbi <strong>m\u1ecdi s\u1ed1 th\u1ef1c<\/strong>, k\u1ec3 c\u1ea3 s\u1ed1 \u00e2m, v\u00e0 m\u1ed7i s\u1ed1 ch\u1ec9 c\u00f3 duy nh\u1ea5t m\u1ed9t c\u0103n b\u1eadc ba. V\u00ed d\u1ee5 \u221b(\u22128) = \u22122 v\u00ec (\u22122)\u00b3 = \u22128, trong khi \u221a(\u22128) kh\u00f4ng t\u1ed3n t\u1ea1i trong t\u1eadp s\u1ed1 th\u1ef1c.<\/p>\n<h2>\u1ee8ng d\u1ee5ng c\u1ee7a c\u0103n b\u1eadc hai<\/h2>\n<p>C\u0103n b\u1eadc hai xu\u1ea5t hi\u1ec7n trong r\u1ea5t nhi\u1ec1u c\u00f4ng th\u1ee9c: t\u00ednh c\u1ea1nh huy\u1ec1n tam gi\u00e1c vu\u00f4ng theo \u0111\u1ecbnh l\u00fd Pytago, t\u00ednh \u0111\u01b0\u1eddng ch\u00e9o h\u00ecnh vu\u00f4ng v\u00e0 h\u00ecnh h\u1ed9p, t\u00ednh kho\u1ea3ng c\u00e1ch gi\u1eefa hai \u0111i\u1ec3m trong h\u1ec7 t\u1ecda \u0111\u1ed9, hay gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh b\u1eadc hai b\u1eb1ng c\u00f4ng th\u1ee9c nghi\u1ec7m c\u00f3 ch\u1ee9a c\u0103n c\u1ee7a bi\u1ec7t th\u1ee9c \u0394. \u0110\u00e2y l\u00e0 ph\u00e9p to\u00e1n kh\u00f4ng th\u1ec3 thi\u1ebfu khi h\u1ecdc h\u00ecnh h\u1ecdc v\u00e0 \u0111\u1ea1i s\u1ed1 \u1edf b\u1eadc THCS v\u00e0 THPT.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-570079\" src=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-4.jpg\" alt=\"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c v\u00e0 b\u00e0i t\u1eadp - \u1ee9ng d\u1ee5ng c\u1ee7a c\u0103n b\u1eadc hai\" width=\"800\" height=\"450\" srcset=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-4.jpg 800w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-4-300x169.jpg 300w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/can-bac-hai-4-768x432.jpg 768w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><\/p>\n<h2>C\u00e2u h\u1ecfi th\u01b0\u1eddng g\u1eb7p v\u1ec1 c\u0103n b\u1eadc hai<\/h2>\n<h3>C\u0103n b\u1eadc hai l\u00e0 g\u00ec?<\/h3>\n<p>C\u0103n b\u1eadc hai c\u1ee7a m\u1ed9t s\u1ed1 a kh\u00f4ng \u00e2m l\u00e0 s\u1ed1 x sao cho x\u00b2 = a. M\u1ed7i s\u1ed1 d\u01b0\u01a1ng c\u00f3 hai c\u0103n b\u1eadc hai \u0111\u1ed1i nhau.<\/p>\n<h3>M\u1ed9t s\u1ed1 d\u01b0\u01a1ng c\u00f3 m\u1ea5y c\u0103n b\u1eadc hai?<\/h3>\n<p>M\u1ed9t s\u1ed1 d\u01b0\u01a1ng c\u00f3 \u0111\u00fang hai c\u0103n b\u1eadc hai l\u00e0 hai s\u1ed1 \u0111\u1ed1i nhau: \u221aa v\u00e0 \u2212\u221aa.<\/p>\n<h3>C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc l\u00e0 g\u00ec?<\/h3>\n<p>C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc l\u00e0 c\u0103n b\u1eadc hai kh\u00f4ng \u00e2m c\u1ee7a m\u1ed9t s\u1ed1, k\u00fd hi\u1ec7u \u221aa. V\u00ed d\u1ee5 c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc c\u1ee7a 25 l\u00e0 5.<\/p>\n<h3>S\u1ed1 \u00e2m c\u00f3 c\u0103n b\u1eadc hai kh\u00f4ng?<\/h3>\n<p>Kh\u00f4ng, s\u1ed1 \u00e2m kh\u00f4ng c\u00f3 c\u0103n b\u1eadc hai trong t\u1eadp s\u1ed1 th\u1ef1c v\u00ec b\u00ecnh ph\u01b0\u01a1ng c\u1ee7a m\u1ecdi s\u1ed1 th\u1ef1c \u0111\u1ec1u kh\u00f4ng \u00e2m.<\/p>\n<h3>\u221a(a\u00b2) b\u1eb1ng bao nhi\u00eau?<\/h3>\n<p>\u221a(a\u00b2) b\u1eb1ng |a|, t\u1ee9c gi\u00e1 tr\u1ecb tuy\u1ec7t \u0111\u1ed1i c\u1ee7a a, ch\u1ee9 kh\u00f4ng ph\u1ea3i lu\u00f4n b\u1eb1ng a.<\/p>\n<h3>Bi\u1ec3u th\u1ee9c \u221aA x\u00e1c \u0111\u1ecbnh khi n\u00e0o?<\/h3>\n<p>Bi\u1ec3u th\u1ee9c \u221aA x\u00e1c \u0111\u1ecbnh khi bi\u1ec3u th\u1ee9c d\u01b0\u1edbi d\u1ea5u c\u0103n kh\u00f4ng \u00e2m, t\u1ee9c l\u00e0 A \u2265 0.<br \/>\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"C\u0103n b\u1eadc hai l\u00e0 g\u00ec?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"C\u0103n b\u1eadc hai c\u1ee7a m\u1ed9t s\u1ed1 a kh\u00f4ng \u00e2m l\u00e0 s\u1ed1 x sao cho x\u00b2 = a. M\u1ed7i s\u1ed1 d\u01b0\u01a1ng c\u00f3 hai c\u0103n b\u1eadc hai \u0111\u1ed1i nhau.\"}},{\"@type\":\"Question\",\"name\":\"M\u1ed9t s\u1ed1 d\u01b0\u01a1ng c\u00f3 m\u1ea5y c\u0103n b\u1eadc hai?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"M\u1ed9t s\u1ed1 d\u01b0\u01a1ng c\u00f3 \u0111\u00fang hai c\u0103n b\u1eadc hai l\u00e0 hai s\u1ed1 \u0111\u1ed1i nhau: \u221aa v\u00e0 \u2212\u221aa.\"}},{\"@type\":\"Question\",\"name\":\"C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc l\u00e0 g\u00ec?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc l\u00e0 c\u0103n b\u1eadc hai kh\u00f4ng \u00e2m c\u1ee7a m\u1ed9t s\u1ed1, k\u00fd hi\u1ec7u \u221aa. V\u00ed d\u1ee5 c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc c\u1ee7a 25 l\u00e0 5.\"}},{\"@type\":\"Question\",\"name\":\"S\u1ed1 \u00e2m c\u00f3 c\u0103n b\u1eadc hai kh\u00f4ng?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Kh\u00f4ng, s\u1ed1 \u00e2m kh\u00f4ng c\u00f3 c\u0103n b\u1eadc hai trong t\u1eadp s\u1ed1 th\u1ef1c v\u00ec b\u00ecnh ph\u01b0\u01a1ng c\u1ee7a m\u1ecdi s\u1ed1 th\u1ef1c \u0111\u1ec1u kh\u00f4ng \u00e2m.\"}},{\"@type\":\"Question\",\"name\":\"\u221a(a\u00b2) b\u1eb1ng bao nhi\u00eau?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"\u221a(a\u00b2) b\u1eb1ng |a|, t\u1ee9c gi\u00e1 tr\u1ecb tuy\u1ec7t \u0111\u1ed1i c\u1ee7a a, ch\u1ee9 kh\u00f4ng ph\u1ea3i lu\u00f4n b\u1eb1ng a.\"}},{\"@type\":\"Question\",\"name\":\"Bi\u1ec3u th\u1ee9c \u221aA x\u00e1c \u0111\u1ecbnh khi n\u00e0o?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Bi\u1ec3u th\u1ee9c \u221aA x\u00e1c \u0111\u1ecbnh khi bi\u1ec3u th\u1ee9c d\u01b0\u1edbi d\u1ea5u c\u0103n kh\u00f4ng \u00e2m, t\u1ee9c l\u00e0 A \u2265 0.\"}}]}<\/script><\/p>\n<h2>K\u1ebft lu\u1eadn<\/h2>\n<p>T\u00f3m l\u1ea1i, <strong>c\u0103n b\u1eadc hai c\u1ee7a a l\u00e0 s\u1ed1 x th\u1ecfa m\u00e3n x\u00b2 = a; c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc \u221aa l\u00e0 c\u0103n kh\u00f4ng \u00e2m, v\u1edbi c\u00e1c t\u00ednh ch\u1ea5t \u221a(ab) = \u221aa\u00b7\u221ab v\u00e0 \u221a(a\u00b2) = |a|<\/strong>. Ghi nh\u1edb b\u1ea3ng c\u0103n b\u1eadc hai c\u00e1c s\u1ed1 ch\u00ednh ph\u01b0\u01a1ng v\u00e0 \u0111i\u1ec1u ki\u1ec7n x\u00e1c \u0111\u1ecbnh A \u2265 0 s\u1ebd gi\u00fap b\u1ea1n t\u00ednh nhanh v\u00e0 tr\u00e1nh sai s\u00f3t. \u0110\u1ec3 h\u1ecdc th\u00eam, m\u1eddi b\u1ea1n tham kh\u1ea3o c\u00e1c b\u00e0i t\u1eadp h\u1ee3p s\u1ed1 nguy\u00ean Z l\u00e0 g\u00ec, kh\u00e1i ni\u1ec7m v\u00e0 \u1ee9ng d\u1ee5ng c\u1ee7a s\u1ed1 nguy\u00ean v\u00e0 c\u00f4ng th\u1ee9c t\u1ed5 h\u1ee3p, ch\u1ec9nh h\u1ee3p tr\u00ean chuy\u00ean m\u1ee5c tin t\u1ee9c c\u1ee7a Ho\u00e0ng H\u00e0 Mobile.<\/p>\n<p>Xem th\u00eam:<\/p>\n<ul>\n<li><a href=\"https:\/\/hoanghamobile.com\/tin-tuc\/cong-thuc-tinh-ap-suat\/\">C\u00f4ng th\u1ee9c t\u00ednh \u00e1p su\u1ea5t p = F\/S v\u00e0 \u00e1p su\u1ea5t ch\u1ea5t l\u1ecfng<\/a><\/li>\n<li><a href=\"https:\/\/hoanghamobile.com\/tin-tuc\/can-bang-phuong-trinh-hoa-hoc\/\">C\u00e1ch c\u00e2n b\u1eb1ng ph\u01b0\u01a1ng tr\u00ecnh h\u00f3a h\u1ecdc nhanh v\u00e0 ch\u00ednh x\u00e1c<\/a><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>C\u0103n b\u1eadc hai c\u1ee7a m\u1ed9t s\u1ed1 a kh\u00f4ng \u00e2m l\u00e0 s\u1ed1 x sao cho x\u00b2 = a; trong \u0111\u00f3 c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc c\u1ee7a a l\u00e0 s\u1ed1 kh\u00f4ng \u00e2m, k\u00fd hi\u1ec7u l\u00e0 \u221aa. V\u00ed d\u1ee5, c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc c\u1ee7a 25 l\u00e0 5 v\u00ec 5\u00b2 = 25. \u0110\u00e2y l\u00e0 ki\u1ebfn th\u1ee9c n\u1ec1n t\u1ea3ng [&hellip;]<\/p>\n","protected":false},"author":102,"featured_media":570080,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_focuskw":"c\u0103n b\u1eadc hai","_yoast_wpseo_title":"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c v\u00e0 b\u00e0i t\u1eadp","_yoast_wpseo_metadesc":"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? T\u00ecm hi\u1ec3u c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c, b\u1ea3ng tra v\u00e0 b\u00e0i t\u1eadp c\u00f3 l\u1eddi gi\u1ea3i chi ti\u1ebft. Xem chi ti\u1ebft t\u1ea1i Ho\u00e0ng H\u00e0 Mobile.","footnotes":""},"categories":[3910,30453],"tags":[],"class_list":["post-570073","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-kham-pha","category-kien-thuc"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v27.3 (Yoast SEO v27.4) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>C\u0103n b\u1eadc hai l\u00e0 g\u00ec? C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c v\u00e0 b\u00e0i t\u1eadp<\/title>\n<meta name=\"description\" content=\"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? T\u00ecm hi\u1ec3u c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c, b\u1ea3ng tra v\u00e0 b\u00e0i t\u1eadp c\u00f3 l\u1eddi gi\u1ea3i chi ti\u1ebft. Xem chi ti\u1ebft t\u1ea1i Ho\u00e0ng H\u00e0 Mobile.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/hoanghamobile.com\/tin-tuc\/can-bac-hai-la-gi\/\" \/>\n<meta property=\"og:locale\" content=\"vi_VN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c v\u00e0 b\u00e0i t\u1eadp\" \/>\n<meta property=\"og:description\" content=\"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? T\u00ecm hi\u1ec3u c\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c, b\u1ea3ng tra v\u00e0 b\u00e0i t\u1eadp c\u00f3 l\u1eddi gi\u1ea3i chi ti\u1ebft. 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C\u0103n b\u1eadc hai s\u1ed1 h\u1ecdc, c\u00f4ng th\u1ee9c v\u00e0 b\u00e0i t\u1eadp\",\"datePublished\":\"2026-07-24T05:50:17+00:00\",\"dateModified\":\"2026-08-25T09:12:52+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/hoanghamobile.com\\\/tin-tuc\\\/can-bac-hai-la-gi\\\/\"},\"wordCount\":1815,\"publisher\":{\"@id\":\"https:\\\/\\\/hoanghamobile.com\\\/tin-tuc\\\/#organization\"},\"image\":{\"@id\":\"https:\\\/\\\/hoanghamobile.com\\\/tin-tuc\\\/can-bac-hai-la-gi\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/hoanghamobile.com\\\/tin-tuc\\\/wp-content\\\/uploads\\\/2026\\\/07\\\/can-bac-hai.jpg\",\"articleSection\":[\"Kh\u00e1m Ph\u00e1\",\"Ki\u1ebfn Th\u1ee9c\"],\"inLanguage\":\"vi\",\"copyrightYear\":\"2026\",\"copyrightHolder\":{\"@id\":\"https:\\\/\\\/hoanghamobile.com\\\/tin-tuc\\\/#organization\"}},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/hoanghamobile.com\\\/tin-tuc\\\/can-bac-hai-la-gi\\\/\",\"url\":\"https:\\\/\\\/hoanghamobile.com\\\/tin-tuc\\\/can-bac-hai-la-gi\\\/\",\"name\":\"C\u0103n b\u1eadc hai l\u00e0 g\u00ec? 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