Trong c\u00e1c tinh th\u1ec3 ng\u01b0\u1eddi ta th\u01b0\u1eddng th\u1ea5y c\u00e1c kh\u1ed1i \u0111a di\u1ec7n \u0111\u1eb7c th\u00f9: c\u00e1c m\u1eb7t c\u1ee7a tinh th\u1ec3 l\u00e0 nh\u1eefng \u0111a di\u1ec7n \u0111\u1ec1u, m\u1ecdi g\u00f3c c\u1ee7a \u0111a di\u1ec7n \u0111\u1ec1u ho\u00e0n to\u00e0n b\u1eb1ng nhau. \u0110\u00f3 ch\u00ednh l\u00e0 c\u00e1c kh\u1ed1i \u0111a di\u1ec7n \u0111\u1ec1u. C\u00f3 r\u1ea5t nhi\u1ec1u kh\u1ed1i \u0111a di\u1ec7n \u0111\u1ec1u, nh\u01b0ng th\u1ef1c ra ch\u00fang \u0111\u01b0\u1ee3c x\u1ebfp th\u00e0nh n\u0103m lo\u1ea1i. T\u1ea1i sao v\u1eady?<\/p>\n\n\n\n
Tr\u01b0\u1edbc h\u1ebft ch\u00fang t\u00f4i xin gi\u1edbi thi\u1ec7u c\u00f4ng th\u1ee9c \u01a0le. V\u00e0o th\u1ebf k\u1ec9 XVII, nh\u00e0 to\u00e1n h\u1ecdc ki\u1ec7t xu\u1ea5t Thu\u1ef5 S\u0129 \u01a0le \u0111\u00e3 ch\u1ec9 ra m\u1ed1i quan h\u1ec7 r\u00e0ng bu\u1ed9c gi\u1eefa s\u1ed1 m\u1eb7t, s\u1ed1 c\u1ea1nh v\u00e0 s\u1ed1 \u0111\u1ec9nh c\u1ee7a kh\u1ed1i \u0111a di\u1ec7n n\u00f3i chung. \u00d4ng n\u00eau ra h\u1ec7 th\u1ee9c gi\u1ea3i t\u00edch<\/p>\n\n\n\n
E = V + F – 2 trong \u0111\u00f3, E l\u00e0 s\u1ed1 c\u1ea1nh, F l\u00e0 s\u1ed1 m\u1eb7t, V l\u00e0 s\u1ed1 \u0111\u1ec9nh c\u1ee7a kh\u1ed1i \u0111a di\u1ec7n.<\/p>\n\n\n\n
Trong to\u00e1n h\u1ecdc ng\u01b0\u1eddi ta g\u1ecdi l\u00e0 c\u00f4ng th\u1ee9c \u01a0le \u0111\u1ec3 ghi nh\u1edb c\u00f4ng lao c\u1ee7a \u00f4ng. B\u00e2y gi\u1edd ch\u00fang ta s\u1ebd v\u1eadn d\u1ee5ng c\u00f4ng th\u1ee9c \u01a0le \u0111\u1ec3 ch\u1ee9ng minh ch\u1ec9 c\u00f3 n\u0103m lo\u1ea1i kh\u1ed1i \u0111a di\u1ec7n.<\/p>\n\n\n\n
Gi\u1ea3 s\u1eed kh\u1ed1i \u0111a di\u1ec7n \u0111\u1ec1u \u0111\u01b0\u1ee3c h\u00ecnh th\u00e0nh t\u1eeb c\u00e1c m\u1eb7t, m\u1ed7i m\u1eb7t c\u00f3 m c\u1ea1nh, s\u1ed1 m\u1eb7t c\u1ee7a kh\u1ed1i \u0111a di\u1ec7n l\u00e0 F, th\u1ebf th\u00ec F m\u1eb7t s\u1ebd c\u00f3 mF c\u1ea1nh, m\u1ed7i c\u1ea1nh l\u1ea1i l\u00e0 c\u1ea1nh chung c\u1ee7a hai m\u1eb7t l\u00e2n c\u1eadn, v\u00ec v\u1eady mF = 2E.<\/p>\n\n\n\n
Gi\u1ea3 s\u1eed m\u1ed7i \u0111a di\u1ec7n \u0111\u1ec1u c\u00f3 c\u00e1c \u0111\u1ec9nh m\u00e0 m\u1ed7i \u0111\u1ec9nh l\u1ea1i l\u00e0 \u0111\u1ec9nh c\u1ee7a m\u1ed9t \u0111a gi\u00e1c \u0111\u1ec1u c\u00f3 n c\u1ea1nh, n\u1ebfu kh\u1ed1i \u0111a di\u1ec7n c\u00f3 V \u0111\u1ec9nh s\u1ebd c\u00f3 nV c\u1ea1nh, m\u1ed7i c\u1ea1nh l\u1ea1i thu\u1ed9c hai \u0111\u1ec9nh n\u00ean nV = 2E.<\/p>\n\n\n\n
Thay c\u00e1c gi\u00e1 tr\u1ecb c\u1ee7a V v\u00e0 F t\u00ednh t\u1eeb hai h\u1ec7 th\u1ee9c v\u1eeba n\u00eau v\u00e0o c\u00f4ng th\u1ee9c \u01a0le \u1edf tr\u00ean ta c\u00f3:<\/p>\n\n\n\n
V\u00e0 sau khi bi\u1ebfn \u0111\u1ed5i ta c\u00f3:<\/p>\n\n\n\n
Ta s\u1ebd b\u1eaft \u0111\u1ea7u x\u00e9t kh\u1ed1i \u0111a di\u1ec7n t\u1ea1o n\u00ean t\u1eeb c\u00e1c tam gi\u00e1c \u0111\u1ec1u. V\u00ec c\u00e1c g\u00f3c c\u1ee7a m\u1eb7t \u0111a di\u1ec7n t\u1ed1i \u0111a kh\u00f4ng th\u1ec3 v\u01b0\u1ee3t qu\u00e1 360o, m\u00e0 m\u1ed7i g\u00f3c c\u1ee7a tam gi\u00e1c \u0111\u1ec1u l\u00e0 60o, n\u00ean kh\u1ed1i \u0111a di\u1ec7n do c\u00e1c tam gi\u00e1c \u0111\u1ec1u t\u1ea1o n\u00ean ch\u1ec9 c\u00f3 th\u1ec3 c\u00f3 ba lo\u1ea1i: g\u00f3c tam di\u1ec7n \u0111\u1ec1u, g\u00f3c t\u1ee9 di\u1ec7n v\u00e0 g\u00f3c ng\u0169 di\u1ec7n. C\u00f2n v\u1edbi c\u00e1c l\u1ee5c gi\u00e1c \u0111\u1ec1u th\u00ec s\u1ebd ra sao? Do 60o 6 = 360o th\u00ec ch\u1ec9 c\u00f3 th\u1ec3 t\u1ea1o m\u1ed9t m\u1eb7t \u0111a gi\u00e1c m\u00e0 kh\u00f4ng t\u1ea1o \u0111\u01b0\u1ee3c kh\u1ed1i \u0111a di\u1ec7n. C\u00f2n v\u1edbi m = 3 ta ch\u1ec9 c\u00f3 ba lo\u1ea1i t\u00ecnh hu\u1ed1ng:<\/p>\n\n\n\n
V\u1edbi n = 3, ta t\u00ednh \u0111\u01b0\u1ee3c E = 6, F = 4 l\u00e0 m\u1ed9t t\u1ee9 di\u1ec7n \u0111\u1ec1u. n = 4, ta t\u00ednh \u0111\u01b0\u1ee3c E = 12, F = 8 l\u00e0 m\u1ed9t kh\u1ed1i b\u00e1t di\u1ec7n \u0111\u1ec1u. n = 5, ta t\u00ednh \u0111\u01b0\u1ee3c E = 30, F = 20 l\u00e0 m\u1ed9t kh\u1ed1i 20 m\u1eb7t.<\/p>\n\n\n\n
Nh\u01b0 v\u1eady, v\u1edbi m\u1eb7t tam gi\u00e1c \u0111\u1ec1u ta ch\u1ec9 c\u00f3 ba lo\u1ea1i: kh\u1ed1i t\u1ee9 di\u1ec7n \u0111\u1ec1u, kh\u1ed1i b\u00e1t di\u1ec7n \u0111i\u1ec1u, kh\u1ed1i 20 m\u1eb7t. Do v\u1eady khi m = 4 v\u00e0 n = 3 thay v\u00e0o c\u00f4ng th\u1ee9c \u01a0le ta c\u00f3:<\/p>\n\n\n\n
E = 12, F = 6.<\/p>\n\n\n\n
Ngh\u0129a l\u00e0 v\u1edbi c\u00e1c m\u1eb7t h\u00ecnh vu\u00f4ng ta ch\u1ec9 t\u1ea1o \u0111\u01b0\u1ee3c kh\u1ed1i l\u1ee5c di\u1ec7n \u0111\u1ec1u.<\/p>\n\n\n\n
Th\u1ebf th\u00ec v\u1edbi c\u00e1c m\u1eb7t ng\u0169 gi\u00e1c \u0111\u1ec1u th\u00ec s\u1ebd ra sao? V\u00ec c\u00e1c g\u00f3c trong c\u1ee7a ng\u0169 gi\u00e1c \u0111\u1ec1u b\u1eb1ng 108o n\u00ean t\u1eeb c\u00e1c ng\u0169 gi\u00e1c \u0111\u1ec1u ta ch\u1ec9 c\u00f3 th\u1ec3 t\u1ea1o \u0111\u01b0\u1ee3c g\u00f3c tam di\u1ec7n \u0111\u1ec1u. V\u00ec v\u1eady khi m = 5, n = 3 thay v\u00e0o c\u00f4ng th\u1ee9c \u01a0le ta s\u1ebd t\u00ednh \u0111\u01b0\u1ee3c:<\/p>\n\n\n\n
E = 30 v\u00e0 F = 12<\/p>\n\n\n\n
Ngh\u0129a l\u00e0 v\u1edbi c\u00e1c m\u1eb7t ng\u0169 gi\u00e1c \u0111\u1ec1u ch\u1ec9 c\u00f3 th\u1ec3 t\u1ea1o th\u00e0nh m\u1ed9t kh\u1ed1i 12 m\u1eb7t.<\/p>\n\n\n\n
Do \u0111\u00f3 c\u00f3 th\u1ec3 th\u1ea5y kh\u1ed1i \u0111a di\u1ec7n \u0111\u1ec1u ch\u1ec9 c\u00f3 n\u0103m lo\u1ea1i: Kh\u1ed1i t\u1ee9 di\u1ec7n \u0111\u1ec1u, kh\u1ed1i l\u1ee5c di\u1ec7n \u0111\u1ec1u, kh\u1ed1i b\u00e1t di\u1ec7n \u0111\u1ec1u, kh\u1ed1i 12 m\u1eb7t \u0111\u1ec1u v\u00e0 kh\u1ed1i 20 m\u1eb7t \u0111\u1ec1u.<\/p>\n\n\n\n
C\u00f2n v\u1edbi m\u1ed9t l\u1ee5c gi\u00e1c \u0111\u1ec1u th\u00ec do l\u1ee5c gi\u00e1c \u0111\u1ec1u c\u00f3 g\u00f3c trong 120o n\u00ean kh\u00f4ng t\u1ea1o \u0111\u01b0\u1ee3c m\u1ed9t g\u00f3c \u0111a di\u1ec7n n\u00ean kh\u00f4ng t\u1ea1o \u0111\u01b0\u1ee3c kh\u1ed1i \u0111a di\u1ec7n \u0111\u1ec1u.<\/p>\n\n\n\n
T\u1eeb kho\u00e1: Kh\u1ed1i \u0111a di\u1ec7n \u0111\u1ec1u; H\u00ecnh \u0111a gi\u00e1c \u0111\u1ec1u; C\u00f4ng th\u1ee9c \u01a0le.<\/p>\n\n\n\n
<\/p>\n\n\n\n\n\n\n","protected":false},"excerpt":{"rendered":"
Trong c\u00e1c tinh th\u1ec3 ng\u01b0\u1eddi ta th\u01b0\u1eddng th\u1ea5y c\u00e1c kh\u1ed1i \u0111a di\u1ec7n \u0111\u1eb7c th\u00f9: c\u00e1c m\u1eb7t c\u1ee7a tinh th\u1ec3 l\u00e0 nh\u1eefng \u0111a di\u1ec7n \u0111\u1ec1u, m\u1ecdi g\u00f3c c\u1ee7a \u0111a di\u1ec7n \u0111\u1ec1u ho\u00e0n to\u00e0n b\u1eb1ng nhau. \u0110\u00f3 ch\u00ednh l\u00e0 c\u00e1c kh\u1ed1i \u0111a di\u1ec7n \u0111\u1ec1u. C\u00f3 r\u1ea5t nhi\u1ec1u kh\u1ed1i \u0111a di\u1ec7n \u0111\u1ec1u, nh\u01b0ng th\u1ef1c ra ch\u00fang \u0111\u01b0\u1ee3c x\u1ebfp […]<\/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-7563","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\/7563","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=7563"}],"version-history":[{"count":0,"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/posts\/7563\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/media?parent=7563"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/categories?post=7563"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vietlearn.org\/kien-thuc\/wp-json\/wp\/v2\/tags?post=7563"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}