cos(θ-π/12)=-4/5,且π/2
问题描述：
cos(θ-π/12)=-4/5,且π/2
答
cos(θ-π/12)=-4/5,sin(θ-π/12)=3/5,sin(2θ-π/6)=-24/25,cos(2θ-π/6)=7/25,
cos(2θ+π/12)=cos(2θ-π/6+π/4)=cos(2θ-π/6)cos(π/4)-sin(2θ-π/6)sin(π/4)=31根号2/50