Trong m\u1ed9t quy\u1ec3n s\u00e1ch to\u00e1n c\u1ea5p hai c\u00f3 m\u1ed9t b\u00e0i to\u00e1n kh\u00e1 l\u00ed th\u00fa sau \u0111\u00e2y: Tr\u00ean m\u1eb7t \u0111\u1ed3ng h\u1ed3 c\u00f3 12 con s\u1ed1, b\u1ea1n h\u00e3y \u0111\u1eb7t c\u00e1c d\u1ea5u c\u1ed9ng (+) d\u1ea5u tr\u1eeb (-) tr\u01b0\u1edbc c\u00e1c con s\u1ed1 \u0111\u1ec3 t\u1ed5ng \u0111\u1ea1i s\u1ed1 c\u1ee7a c\u00e1c con s\u1ed1 b\u1eb1ng kh\u00f4ng. B\u1ea1n c\u00f3 th\u1ec3 th\u1ef1c hi\u1ec7n \u0111\u01b0\u1ee3c y\u00eau c\u1ea7u \u0111\u00f3 kh\u00f4ng?<\/p>\n\n\n\n
Th\u1ef1c ra b\u1ea1n ch\u1ec9 c\u1ea7n suy ngh\u0129 m\u1ed9t ch\u00fat c\u00f3 th\u1ec3 t\u00ecm ngay \u0111\u01b0\u1ee3c m\u1ed9t \u0111\u00e1p \u00e1n: Tr\u01b0\u1edbc c\u00e1c con s\u1ed1 1, 2, 3, 4, 5, 7, 8, 9 \u0111\u1eb7t d\u1ea5u c\u1ed9ng (+) c\u00f2n tr\u01b0\u1edbc c\u00e1c con s\u1ed1 6, 10, 11, 12 \u0111\u1eb7t d\u1ea5u tr\u1eeb (-), do \u0111\u00f3 ta c\u00f3: 1 + 2 + 3 + 4 + 5 + 7 + 8 + 9 + (-6, -10, -11, -12) = 39 – 39 = 0. Do \u0111\u00f3 ta th\u1ea5y \u0111\u00f3 l\u00e0 \u0111\u00e1p \u00e1n \u0111\u00fang.<\/p>\n\n\n\n
B\u00e0i to\u00e1n n\u00e0y c\u00f3 124 \u0111\u00e1p \u00e1n n\u00ean vi\u1ec7c t\u00ecm h\u1ebft \u0111\u01b0\u1ee3c c\u00e1c \u0111\u00e1p \u00e1n kh\u00f4ng ph\u1ea3i m\u1ed9t vi\u1ec7c d\u1ec5. Nh\u01b0ng n\u1ebfu ch\u00fa \u00fd b\u1ea1n c\u00f3 th\u1ec3 t\u00ecm \u0111\u01b0\u1ee3c quy lu\u1eadt v\u00e0 c\u00f3 th\u1ec3 t\u00ecm \u0111\u01b0\u1ee3c nhi\u1ec1u \u0111\u00e1p \u00e1n.<\/p>\n\n\n\n
Tr\u01b0\u1edbc h\u1ebft ta bi\u1ebft r\u1eb1ng m\u1ed9t c\u1eb7p s\u1ed1 c\u00f9ng gi\u00e1 tr\u1ecb b\u1eb1ng s\u1ed1 nh\u01b0ng tr\u00e1i d\u1ea5u th\u00ec t\u1ed5ng c\u1ee7a ch\u00fang b\u1eb1ng kh\u00f4ng. Ta l\u1ea1i bi\u1ebft 1 + 2 + 3 +\u2026 + 12 = 78 n\u00ean ch\u1ec9 c\u1ea7n ph\u00e2n 12 s\u1ed1 th\u00e0nh hai nh\u00f3m, m\u1ed7i nh\u00f3m c\u00f3 t\u1ed5ng b\u1eb1ng 39, sau \u0111\u00f3 ta \u0111\u1eb7t d\u1ea5u ng\u01b0\u1ee3c nhau tr\u01b0\u1edbc m\u1ed7i nh\u00f3m: tr\u01b0\u1edbc m\u1ed9t nh\u00f3m ta \u0111\u1eb7t d\u1ea5u d\u01b0\u01a1ng (+) c\u00f2n tr\u01b0\u1edbc nh\u00f3m kia ta \u0111\u1eb7t d\u1ea5u \u00e2m (-) th\u00ec s\u1ebd l\u00e0m t\u1ed5ng \u0111\u1ea1i s\u1ed1 c\u1ee7a 12 con s\u1ed1 s\u1ebd b\u1eb1ng kh\u00f4ng.<\/p>\n\n\n\n
Hai l\u00e0 ba s\u1ed1 l\u1edbn nh\u1ea5t trong 12 con s\u1ed1 c\u00f3 t\u1ed5ng s\u1ed1 l\u00e0 10 + 11 + 12 = 33 nh\u1ecf h\u01a1n 39; c\u00f2n t\u1ed5ng c\u1ee7a c\u00e1c s\u1ed1 nh\u1ecf c\u00f2n l\u1ea1i l\u00e0 1 + 2 + 3 +\u2026+ 9 = 45 l\u1edbn h\u01a1n 39 n\u00ean khi chia c\u00e1c s\u1ed1 th\u00e0nh nh\u00f3m th\u00ec \u00edt nh\u1ea5t c\u00f3 th\u1ec3 l\u00e0 b\u1ed1n s\u1ed1 v\u00e0 s\u1ed1 con s\u1ed1 t\u1ed1i \u0111a trong m\u1ed9t nh\u00f3m s\u1ed1 l\u00e0 t\u00e1m, nh\u01b0 v\u1eady s\u1ed1 c\u00e1c con s\u1ed1 trong m\u1ed9t nh\u00f3m ch\u1ec9 c\u00f3 th\u1ec3 l\u00e0 4 v\u00e0 8, 5 v\u00e0 7, 6 v\u00e0 6.<\/p>\n\n\n\n
Ba l\u00e0 gi\u1ea3 s\u1eed ta chia 12 con s\u1ed1 n\u00e0y th\u00e0nh hai nh\u00f3m l\u00e0 A v\u00e0 B m\u1ed7i nh\u00f3m c\u00f3 t\u1ed5ng c\u00e1c s\u1ed1 l\u00e0 39, v\u1edbi nh\u00f3m A ta \u0111\u00e1nh d\u1ea5u c\u1ed9ng (+) tr\u01b0\u1edbc m\u1ed7i con s\u1ed1 v\u00e0 nh\u00f3m kia ta \u0111\u1eb7t d\u1ea5u tr\u1eeb (-), nh\u01b0 v\u1eady ta s\u1ebd c\u00f3 hai \u0111\u00e1p \u00e1n. V\u00ed nh\u01b0 (+1, +2, +3, +4, +6, +11, +12); (-5, -7, – 8, -9, -10) v\u00e0 (-1, -2, -3, -4, -6, -11, -12); (+5, +7, +8, +9, +10)<\/p>\n\n\n\n
B\u1ea1n h\u00e3y d\u1ef1a v\u00e0o quy lu\u1eadt tr\u00ean v\u00e0 th\u1eed t\u00ecm xem.<\/p>\n\n\n\n
T\u1eeb kho\u00e1: T\u1ed5ng \u0111\u1ea1i s\u1ed1.<\/p>\n\n\n\n
<\/p>\n\n\n\n\n\n\n","protected":false},"excerpt":{"rendered":"
Trong m\u1ed9t quy\u1ec3n s\u00e1ch to\u00e1n c\u1ea5p hai c\u00f3 m\u1ed9t b\u00e0i to\u00e1n kh\u00e1 l\u00ed th\u00fa sau \u0111\u00e2y: Tr\u00ean m\u1eb7t \u0111\u1ed3ng h\u1ed3 c\u00f3 12 con s\u1ed1, b\u1ea1n h\u00e3y \u0111\u1eb7t c\u00e1c d\u1ea5u c\u1ed9ng (+) d\u1ea5u tr\u1eeb (-) tr\u01b0\u1edbc c\u00e1c con s\u1ed1 \u0111\u1ec3 t\u1ed5ng \u0111\u1ea1i s\u1ed1 c\u1ee7a c\u00e1c con s\u1ed1 b\u1eb1ng kh\u00f4ng. B\u1ea1n c\u00f3 th\u1ec3 th\u1ef1c hi\u1ec7n \u0111\u01b0\u1ee3c y\u00eau […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_disable_autopaging":false},"categories":[15,9],"tags":[],"class_list":["post-7527","post","type-post","status-publish","format-standard","hentry","category-hoi-dap-khoa-hoc","category-toan-hoc"],"_links":{"self":[{"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/posts\/7527","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/comments?post=7527"}],"version-history":[{"count":0,"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/posts\/7527\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/media?parent=7527"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/categories?post=7527"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/tags?post=7527"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}