sin²a+cos²a=1sina=±4/5cos^2(a/2+π/4)+2sin^2(a/2-π/4)=[1+cos2(a/2+π/4)]/2+2[1-cos2(a/2-π/4)]/2=[1+cos(a+π/2)]/2+2[1-cos(a-π/2)]/2=(1-sina)/2+2(1-sina)/2=3/2-3sina/2所以原式=39/10或-9/1...