- 急，在线等已知a向量=(cosα,sinα),b向量=(cosβ
- 已知a向量=(cα,sinα),b向量=(cosβ,sinβ).若a向量×b向量=4/5,α=π/8,求tan(α+β)的??
- cos(a)cos(b)+sin(a)sin(b)=cos(a-b) =4/5;
sin(a-b) =+/-3/5;
tan(a-b) =+/- 3/4;
tan(2a) =1;
tan(b+a) = tan(b-a+2a)
= (tan(b-a)+tan(2a)/(1-tan(2a)tan(b-a)
=7或 1/7