Question

[Pham Trong Bach]

Cho tam giác ABC. Tính tổng  $\left(\stackrel{\to }{AB},\stackrel{\to }{BC}\right)+\left(\stackrel{\to }{BC},\stackrel{\to }{CA}\right)+\left(\stackrel{\to }{CA},\stackrel{\to }{AB}\right).$

A. $180°$

B. $360°$

C. $270°$

D. $120°$

Answer 1

[Cao Minh Tâm]

Ta có  A B → , B C → = 180 0 − A B C ^ B C → , C A → = 180 0 − B C A ^ C A → , A B → = 180 0 − C A B ^

⇒ A B → , B C → + B C → , C A → + C A → , A B → = 540 0 − A B C ^ + B C A ^ + C A B ^ = 540 0 − 180 0 = 360 0 .

Chọn B.