已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a等于多少
问题描述:
已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a等于多少
已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a .
答
已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a
2sina=-cosa
tana=-1/2
(1+2sinacosa)/(sin^2a-cos^2a)
=(sina+cosa)^2/[(sina+cosa)(sina-cosa)]
=(sina+cosa)/(sina-cosa)(分子分母同时除以cosa)
=(tana+1)/(tana-1)
=(-1/2+1)/(-1/2-1)
=-1/3