tan(X+45度)=1/3,(sinX-cosX)^2/cos2x?

问题描述:

tan(X+45度)=1/3,(sinX-cosX)^2/cos2x?
A.3
B.-3
C.2
D.-2

(sinx-cosx)^2/cos2x
=(sinx-cosx)/(cos^2x-sin^2x)
=(sinx-cosx)/(sinx+cosx)
=(tanx-1)/(1+tanx)
=tan(x-45°)=1/3