化简cos2(α-π/4)+cos2(α+π/4)

分类: 作业答案 • 2022-04-12 08:53:37

问题描述：

答

原式=cos(2a-π/2)+cos(2a+π/2)
=sin[π/2-(2a-π/2)]+sin[π/2-(2a+π/2)]
=sin(π-2a)+sin(-2a)
=sin2a-sin2a
=0

答

cos2(α-π/4)+cos2(α+π/4)
=cos(2α-π/2)+cos(2α+π/2)
=sin2a-sin2a
=0