Tam gi\u00e1c th\u01b0\u1eddng \u0111\u01b0\u1ee3c t\u00ednh b\u1eb1ng c\u00e1ch l\u1ea5y chi\u1ec3u cao nh\u00e2n v\u1edbi \u0111\u1ed9 d\u00e0i c\u1ea1nh \u0111\u00e1y sau \u0111\u00f3 t\u1ea5t c\u1ea3 \u0111em chia cho hai. Hay n\u00f3i c\u00e1ch kh\u00e1c \u0111\u1ec3 t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c th\u01b0\u1eddng s\u1ebd b\u1eb1ng 1\/3 t\u00edch c\u1ee7a chi\u1ec3u cao v\u00e0 chi\u1ec1u d\u00e0i c\u1ea1nh \u0111\u00e1y c\u1ee7a tam gi\u00e1c.<\/p>\n
![\"\"](\"https:\/\/onthitot.com\/wp-content\/uploads\/2018\/09\/tong-hop-cong-thuc-tinh-dien-tich-tam-giac..png\")
<\/p>\n
C\u00f4ng th\u1ee9c: S= (A x h)\/2<\/p>\n
Trong \u0111\u00f3:<\/p>\n
A: l\u00e0 chi\u1ec1u d\u00e0i c\u1ee7a \u0111\u00e1y tam gi\u00e1c ( n\u00f3 l\u00e0 m\u1ed9t trong 3 c\u1ea1nh c\u1ee7a tam gi\u00e1c t\u00f9y theo quy \u0111\u1ecbnh \u0111\u1eb7t c\u1ee7a ng\u01b0\u1eddi t\u00ednh)<\/p>\n
H: Ch\u00ednh l\u00e0 chi\u1ec3u cao c\u1ee7a h\u00ecnh tam gi\u00e1c, \u1ee9ng v\u1edbi ph\u1ea7n \u0111\u00e1y chi\u1ebfu l\u00ean ( chi\u1ec1u cao c\u1ee7a tam gi\u00e1c b\u1eb1ng \u0111o\u1ea1n th\u1eb3ng h\u1ea1 t\u1eeb \u0111\u1ec9nh xu\u1ed1ng, v\u00e0 vu\u00f4ng g\u00f3c v\u1edbi \u0111\u00e1y c\u1ee7a tam gi\u00e1c.<\/p>\n
C\u00f4ng th\u1ee9c suy ra: H = (S x 2) ho\u1eb7c a=(Sx2)\/h<\/p>\n
\u0110\u1ed1i v\u1edbi tr\u01b0\u1eddng h\u1ee3p kh\u00f4ng cho c\u1ea1nh \u0111\u00e1y ho\u1eb7c chi\u1ec1u cao m\u00e0 cho tr\u01b0\u1edbc di\u1ec7n t\u00edch v\u00e0 c\u1ea1nh c\u00f2n l\u1ea1i c\u00f2n lai th\u00ec c\u00e1c b\u1ea1n h\u00e3y \u00e1p d\u1ee5ng c\u00f4ng th\u1ee9c suy ra \u1edf tr\u00ean \u0111\u1ec3 t\u00ednh nh\u00e9.<\/p>\n
C\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c vu\u00f4ng<\/strong><\/p>\n C\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c vu\u00f4ng t\u01b0\u01a1ng t\u1ee5 v\u1edbi c\u00e1ch t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c th\u01b0\u1eddng. Nso s\u1ebd b\u1eb1ng \u00bd t\u00edch c\u1ee7a chi\u1ec3u cao v\u1edbi chi\u1ec1u dai c\u1ea1nh \u0111\u00e1y. Tuy nhi\u00ean, h\u00ecnh tam gi\u00e1c vu\u00f4ng s\u1ebd kh\u00e1c bi\u1ec7t h\u01a1n so v\u1edbi tam gi\u00e1c th\u01b0\u1eddng do th\u1ec3 hi\u1ec7n r\u00f5 chi\u1ec1u chi\u1ec1u cao v\u00e0 chi\u1ec1u d\u00e0i c\u1ea1nh \u0111\u00e1y, c\u00e1c b\u1ea1n kh\u00f4ng ph\u1ea3i v\u1ebd th\u00eam \u0111\u1ec3 t\u00ednh th\u00eam chi\u1ec1u cao c\u1ee7a tam gi\u00e1c.<\/p>\n C\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c vu\u00f4ng\u00a0 trong to\u00e1n h\u1ecdc<\/strong><\/p>\n S= (a x h)\/2<\/p>\n Trong \u0111\u00f3:<\/p>\n A: l\u00e0 chi\u00eau d\u00e0i c\u1ee7a \u0111\u00e1y tam gi\u00e1c vu\u00f4ng ( \u0111\u00e1y c\u1ee7a tam gi\u00e1c vu\u00f4ng l\u00e0 m\u1ed9t trong 3 c\u1ea1nh c\u1ee7a tam gi\u00e1c v\u00e0 vu\u00f4ng g\u00f3c v\u1edbi m\u1ed9t c\u1ea1nh c\u00f2n l\u1ea1i c\u1ee7a tam gi\u00e1c)<\/p>\n H: ch\u00ednh l\u00e0 chi\u1ec3u d\u00e0i c\u1ee7a tam gi\u00e1c, \u1ee9ng v\u1edbi v\u1edbi ph\u1ea7n \u0111\u00e1y \u1ee9ng l\u00ean chi\u1ec3u cao (chi\u1ec1u cao tam gi\u00e1c b\u1eb1ng \u0111o\u1ea1n th\u1eb3ng h\u1ea1 th\u1eb3ng t\u1eeb \u0111\u1ec9nh xu\u1ed1ng xu\u1ed1ng c\u1ea1nh \u0111\u00e1y v\u00e0 \u0111\u1ed3ng th\u1eddi \u0111\u1ed3ng th\u1eddi n\u00f3 c\u0169ng vu\u00f4ng g\u00f3c v\u1edbi \u0111\u00e1y.<\/p>\n C\u00f4ng th\u1ee9c suy ra: H=(sx2) ho\u1eb7c A = (Sx2)\/h<\/p>\n N\u1ebfu nh\u01b0 c\u00f3 c\u00e2u h\u1ecfi ng\u01b0\u1ee3c v\u1ec1 c\u00e1ch t\u00ednh chi\u1ec3u d\u00e0i c\u1ea1nh \u0111\u00e1y ho\u1eb7c chi\u1ec1u cao th\u00ec c\u00e1c b\u1ea1n c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng c\u00f4ng th\u1ee9c suy ra \u1edf tr\u00ean.<\/p>\n C\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00ednh tam gi\u00e1c c\u00e2n trong to\u00e1n h\u1ecdc<\/strong><\/p>\n Tam gi\u00e1c c\u00e2n l\u00e0 tam gi\u00e1c trong \u0111\u00f3 c\u00e1c c\u1ea1nh b\u00ean v\u00e0 hai g\u00f3c b\u1eb1ng nhau. Trong \u0111\u00f3 c\u00e1ch t\u00ednh di\u1ec7n t\u00ednh tam gi\u00e1c c\u00e2n c\u0169ng t\u01b0\u01a1ng t\u1ee5 c\u00e1ch t\u00ednh tam th\u01b0\u1eddng n\u1ebfu nh\u01b0 ch\u00fang ta bi\u1ebft chi\u1ec1u cao c\u1ee7a tam gi\u00e1c v\u00e0 \u0111\u00e1y.<\/p>\n Di\u1ec5n gi\u1ea3i: Di\u1ec7n t\u00edch tam gi\u00e1c c\u00e2n b\u1eb1ng t\u00edch c\u1ee7a chi\u1ec3u cao n\u1ed1i t\u1eeb \u0111\u1ec9nh tam gi\u00e1c \u0111\u00f3 t\u1edbi c\u1ea1nh \u0111\u00e1y tam gi\u00e1c sai \u0111\u00f3 chia 2.<\/p>\n C\u00f4ng th\u1ee9c: S = (a x h)\/2<\/p>\n A; l\u00e0 chi\u1ec1u d\u00e0i \u0111\u00e1y tam gi\u00e1c c\u00e2n ( \u0111\u00e1y l\u00e0 m\u1ed9t trong 3 c\u1ea1nh c\u1ee7a tam gi\u00e1c)<\/p>\n H: l\u00e0 chi\u1ec1u cao c\u1ee7a tam gi\u00e1c ( chi\u1ec1u cao tam gi\u00e1c b\u1eb1ng \u0111o\u1ea1n th\u1eb3ng h\u1ea1 t\u1eeb \u0111\u1ec9nh xu\u1ed1ng \u0111\u00e1y)<\/p>\n C\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c \u0111\u1ec1u<\/p>\n Tam gi\u00e1c \u0111\u1ec1u l\u00e0 tam gi\u00e1c c\u00f3 3 c\u1ea1nh b\u1eb1ng nhau v\u00e0 m\u1ed7i g\u00f3c b\u1eb1ng nhau, b\u1ea5t c\u1ee9 tam gi\u00e1c n\u00e0o c\u00f3 ba g\u00f3c b\u1eb1ng nhau c\u0169ng \u0111\u01b0\u1ee3c xem l\u00e0 m\u1ed9t tam gi\u00e1c \u0111\u1ec1u.<\/p>\n C\u00f4ng\u00a0 th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c \u0111\u1ec1u<\/p>\n S= A2 <\/sup>x 3().<\/p>\n Trong \u0111\u00f3:<\/p>\n A: Chi\u1ec1u d\u00e0i m\u1ed9t c\u1ea1nh b\u1ea5t k\u1ef3 trong tam gi\u00e1c \u0111\u1ec1u<\/p>\n B\u00e0i t\u1eadp 1:<\/strong><\/p>\n Cho m\u1ed9t h\u00ecnh tam gi\u00e1c ABC, trong \u0111\u00f3 c\u00f3 chi\u1ec1u cao n\u1ed1i t\u1eeb \u0111\u1ec9nh \u1ea2nh xu\u1ed1ng \u0111\u00e1y BC b\u1eb1ng 3, chi\u1ec1u d\u00e0i \u0111\u00e1y BC b\u1eb1ng 6. T\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c th\u01b0\u1eddng ABC? (\u0110\u01a1n v\u1ecb t\u00ednh: cm)<\/p>\n \u0110\u00e1p \u00e1n<\/strong>: G\u1ecdi a =6 v\u00e0 h=3.<\/p>\n Suy ra\u00a0S\u00a0<\/strong>= (a x h)\/ 2 = (6×3)\/2 ho\u1eb7c 1\/2 x (6×3) =\u00a09 cm<\/strong><\/p>\n B\u00e0i t\u1eadp 2:<\/strong><\/p>\n – V\u00ed d\u1ee5:\u00a0<\/strong>C\u00f3 m\u1ed9t h\u00ecnh tam gi\u00e1c vu\u00f4ng ABC, vu\u00f4ng g\u00f3c nhau t\u1ea1i \u0111i\u1ec3m B, chi\u1ec1u d\u00e0i c\u1ea1nh \u0111\u00e1y BC l\u00e0 5 cm, chi\u1ec1u cao l\u00e0 2 cm. H\u1ecfi di\u1ec7n t\u00edch c\u1ee7a h\u00ecnh tam gi\u00e1c vu\u00f4ng ABC b\u1eb1ng bao nhi\u00eau? \u0110\u01a1n v\u1ecb t\u00ednh: cm.<\/p>\n \u0110\u00e1p \u00e1n<\/strong>: G\u1ecdi a =5 v\u00e0 h=2.<\/p>\n Suy ra\u00a0S\u00a0<\/strong>= (a x h)\/ 2 = (5×2)\/2 ho\u1eb7c 1\/2 x (5×2) =\u00a05 cm<\/strong><\/p>\n B\u00e0i t\u1eadp 3:<\/strong><\/p>\n Cho m\u1ed9t tam gi\u00e1c c\u00e2n ABC c\u00f3 chi\u1ec1u cao n\u1ed1i t\u1eeb \u0111\u1ec9nh A xu\u1ed1ng \u0111\u00e1y BC b\u1eb1ng 7 cm, chi\u1ec1u d\u00e0i \u0111\u00e1y cho l\u00e0 6 cm. H\u1ecfi di\u1ec7n t\u00edch c\u1ee7a tam gi\u00e1c c\u00e2n ABC b\u1eb1ng bao nhi\u00eau.<\/p>\n G\u1ecdi a =6 v\u00e0 h=7.<\/p>\n Suy ra\u00a0S\u00a0<\/strong>= (a x h)\/ 2 = (6×7)\/2 ho\u1eb7c 1\/2 x (6×7) =\u00a021 cm<\/strong><\/p>\n B\u00e0i t\u1eadp 4:<\/strong><\/p>\n C\u00f3 m\u1ed9t tam gi\u00e1c \u0111\u1ec1u ABC v\u1edbi chi\u1ec1u d\u00e0i c\u00e1c c\u1ea1nh b\u1eb1ng nhau l\u00e0 9 cm, bi\u1ebft c\u00e1c g\u00f3c c\u1ee7a tam gi\u00e1c n\u00e0y \u0111\u1ec1u b\u1eb1ng 60 \u0111\u1ed9. H\u1ecfi di\u1ec7n t\u00edch tam gi\u00e1c \u0111\u1ec1u ABC b\u1eb1ng bao nhi\u00eau?<\/p>\n \u0110\u00e1p \u00e1n<\/strong>: Do m\u1ed7i c\u1ea1nh AB = AC = BC = 9 n\u00ean ta c\u00f3 chi\u1ec1u d\u00e0i c\u1ea1nh a = 9.<\/p>\n Thay v\u00e0o c\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c \u0111\u1ec1u ta c\u00f3:\u00a0S<\/strong>\u00a0= a2<\/sup>\u00a0x (\u221a3)\/4 = S = 92<\/sup>\u00a0x (\u221a3)\/4\u00a0 = 81 x\u00a0 (\u221a3)\/4 = 81 x\u00a0 (1,732\/4) =\u00a035,07 cm<\/strong><\/p>\n B\u00ean c\u1ea1nh \u0111\u00f3 c\u00f3 r\u1ea5t nhi\u1ec1u c\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c khi ng\u01b0\u1eddi d\u00f9ng bi\u1ebft \u0111\u01b0\u1ee3c t\u1ea5t c\u1ea3 c\u00e1c c\u1ea1nh. V\u00ed d\u1ee5 nh\u01b0 s\u1eed d\u1ee5ng c\u00f4ng th\u1ee9c Heron, t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c b\u1eb1ng g\u00f3c v\u00e0 h\u00e0m l\u01b0\u1ee3ng gi\u00e1c.<\/p>\n D\u00f9 c\u00e1c b\u1ea1n s\u1eed d\u1ee5ng c\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c n\u00e0o \u0111i ch\u0103ng n\u1eefa th\u00ec c\u00e1c b\u1ea1n c\u0169ng c\u1ea7n ph\u1ea3i bi\u1ebft r\u1eb1ng kh\u00f4ng ph\u1ea3i l\u00fac n\u00e0o chi\u1ec1u cao c\u0169ng n\u1eb1m trong tam gi\u00e1c, l\u00fac n\u00e0y c\u1ea7n v\u1ebd th\u00eam chi\u1ec3u cao v\u00e0 c\u1ea1nh \u0111\u00e1y b\u1ed5 sung.<\/p>\n","protected":false},"excerpt":{"rendered":" C\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c l\u00e0 m\u1ed9t trong nh\u1eefng c\u00f4ng th\u1ee9c \u0111\u01b0\u1ee3c r\u1ea5t nhi\u1ec1u b\u1ea1n quan t\u00e2m. N\u1ebfu nh\u01b0 ch\u00fang ta mu\u1ed1n gi\u1ea3i \u0111\u01b0\u1ee3c c\u00e1c b\u00e0i t\u1eadp n\u00e0y… <\/p>\n","protected":false},"author":9,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[418,407],"tags":[],"amp_enabled":true,"_links":{"self":[{"href":"https:\/\/onthitot.com\/wp-json\/wp\/v2\/posts\/9982"}],"collection":[{"href":"https:\/\/onthitot.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/onthitot.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/onthitot.com\/wp-json\/wp\/v2\/users\/9"}],"replies":[{"embeddable":true,"href":"https:\/\/onthitot.com\/wp-json\/wp\/v2\/comments?post=9982"}],"version-history":[{"count":0,"href":"https:\/\/onthitot.com\/wp-json\/wp\/v2\/posts\/9982\/revisions"}],"wp:attachment":[{"href":"https:\/\/onthitot.com\/wp-json\/wp\/v2\/media?parent=9982"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/onthitot.com\/wp-json\/wp\/v2\/categories?post=9982"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/onthitot.com\/wp-json\/wp\/v2\/tags?post=9982"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}M\u1ed9t s\u1ed1 b\u00e0i t\u1eadp \u1ee9ng d\u1ee5ng c\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch tam gi\u00e1c<\/strong><\/h3>\n