cos的四次方二分之x减去sin四次方二分之x

问题描述:

cos的四次方二分之x减去sin四次方二分之x

cos^4(x/2)-sin^4(x/x)
=[cos²(x/2)+sin²(x/2)][cos²(x/2)-sin²(x/2)]
=cos²(x/2)-sin²(x/2)
=cosx