预备知识 cos(A-B)=cosAcosB+sinAsinBcos(A+B)=cosAcosB-sinAsinBcos(A-B)-cos(A+B)=2sinAsinB∴ sinAsinB=1/2[cos(A-B)-cos(A+B)]∫sin3xsinxdx=1/2 ∫(cos2x-cos4x)dx=1/4 sin2x -1/8 sin8x +C
