已知向量a=(cosα,-2),b=(sinα,1),且a//b,则tan(α-π/4)=?
问题描述:
已知向量a=(cosα,-2),b=(sinα,1),且a//b,则tan(α-π/4)=?
A.3B.-3 C.1/3D.-1/3
答
cosa/-2=sina/1
-0.5=sina/cosa
tana=-0.5
tan(a-π/4)=(tana-tanπ/4)/(1-tana*tanπ/4)=(tana-1)/(1-tana)=-2.25选择:A.3B.-3 C.1/3D.-1/3=(tana-tanπ/4)/(1+tana*tanπ/4)=-1.5/0.5=-3不好意思啊,小细节算错了