若sinθ+sin^2θ=1,求cos^2θ+cos^6θ+cos^8θ=?
问题描述:
若sinθ+sin^2θ=1,求cos^2θ+cos^6θ+cos^8θ=?
答
sinθ+sin^2θ=1
cos^2θ=sinθ
cos^2θ+cos^6θ+cos^8θ=sinθ+sin^3θ+sin^4θ=sinθ+sinθ(1-sinθ)+(1-sinθ)^2=1