已知sin(x-π/4)=3/5,∈(π/4,π/2),求cos2x的值?如题.是x∈(π/4,π/2)

问题描述:

已知sin(x-π/4)=3/5,∈(π/4,π/2),求cos2x的值?
如题.
是x∈(π/4,π/2)