已知,cos(x-π/4)=√2/10,x属于(π/2,3π/4),求cos(2x+π/3)的值cos(x-π/4)=√2/2(cosx+sinx)=√2/10 ,sinx+cosx=1/5 ,1+sin2x=1/25,sin2x=-24/25 ,cos2x=-7/25cos(2x+π/3)=1/2cos2x-√3/2sin2x=(-7/50)+24√3/50=...