已知cos(α+π/4)=3/5,α∈[π/2,3π/2),求cos(2α+π/4)
问题描述:
已知cos(α+π/4)=3/5,α∈[π/2,3π/2),求cos(2α+π/4)
答
cos(2α π/4)=cos(2α)*cos(π/4)-sin2α*sin(π/4)
再把cos(α π/4)=3/5化简cos(α π/4)=cos(α)*cos(π/4)-sinα*sin(π/4)=3/5
根据这两个等式就可以得出.