若sin(270度+θ)=2cos(90度+θ),则cos^2+sinθcosθ-sin^2θ的值为
问题描述:
若sin(270度+θ)=2cos(90度+θ),则cos^2+sinθcosθ-sin^2θ的值为
答
cosθ=-2sinθ
sinθ^2+cosθ^2=1
5sinθ^2=1
sinθ^2=1/5
cosθ^2+sinθcosθ-sinθ^2
=4sinθ^2-2sinθ^2-sinθ^2
=sinθ^2
=1/5