已知sin(x+π/12),x∈(π/2,π),求sin2x,cos2x
问题描述：
已知sin(x+π/12),x∈(π/2,π),求sin2x,cos2x
sin(x+π/12）=3/5
答
sin(x+π/12）＝3/5,cos(x+π/12）=-4/5sin2（x+π/12)=2sin(x+π/12）cos(x+π/12）=-24/25sin2（x+π/12)=sin（2x+π/6）=√3/2sin2x+1/2cos2x=-24/25cos2（x+π/12)=√3/2cos2x-1/2sin2x=7/25sin2x=cos2x=接下来...