cos[(π/4)-x]=sin{(π/2)-[(π/4)-x]}=sin[(π/4)+x]=-3/5∴sin[(π/4)+x]=-3/5sin2x=cos[(π/2)-2x]=cos2[(π/4)-x]=2*{cos[(π/4)-x]}^2-1=2*(9/25)-1=-7/25sin2x/（sin（x+π/4））= 7/15