(2/2)量a.b平行,则tan(A-圆周率/4)=?

问题描述:

(2/2)量a.b平行,则tan(A-圆周率/4)=?

向量a=(cosA,-2),b=(sinA,1)且向量a.b平行,
所以
sinA/cosA=-1/2=tanA
tan(A-圆周率/4)=(tanA-tanπ/4)/(1+tanAtanπ/4)
=(-1/2-1)/(1-1/2)
=-3