CHO A= ( –2; –1) ; B= ( 4; –3 ). COS(A; B) =

Câu 28: Cho

a

= ( –2; –1) ;

b

= ( 4; –3 ). cos(

a

;

b

) = ? A. –

5

5

C.

3

2

D.

1

2

5

B. 2

5