cos8θ-sin8θ=?
问题描述：
cos8θ-sin8θ=?
答
左边=(sinθ)^8+(cosθ)^8+2(sinθcosθ)^4-2(sinθcosθ)^4=[(sinθ)^4-(cosθ)^4]^2+2(sinθcosθ)^4=[(sin^2θ+cos^2θ)(sin^2θ-cos^2θ)]^2+2(sinθcosθ)^4=[(sinθ)^2-(cosθ)^2]^2+2(sinθ)^4(cosθ)^4=(sin...