sinθ=12/13,则cos^4θ-sin^4θ
问题描述：
sinθ=12/13,则cos^4θ-sin^4θ
答
∵sinθ=12/13
∴cosθ=±5/13
cos^4θ-sin^4θ
=(cos^2θ + sin^2θ)(cos^2θ - sin^2θ)
=cos^2θ - sin^2θ
=25/169 - 144/169
= -119/169