cos^2(π/4+α)=(cos(π/4)cosα-sin(π/4)sinα)²

问题描述:

cos^2(π/4+α)=(cos(π/4)cosα-sin(π/4)sinα)²
cos^2(π/4+α)是怎么等于(cos(π/4)cosα-sin(π/4)sinα)²的?

因为cos(π/4+α)=(cos(π/4)cosα-sin(π/4)sinα)
所以cos^2(π/4+α)=(cos(π/4)cosα-sin(π/4)sinα)²这是哪本书里的公式,高一上学期有学到么cos(a+b)=cosacosb-sinasinb是个公式