令 x/2=t x=2t dx=2dt ∫cosxsin(x/2)dx=∫2cos(2t)sintdt=2∫-cos(2t)dcost=2∫-(2cos^2t-1)dcost=2∫-2cos^2t+1dcost=2(-2cos^3t/3+cost)+C =-4cos^2t/3+2cost+C=-4cos^3(x/2)/3+2cos(x/2)+C
