∫[-π/2,0]5cosθd(5sinθ+3)=25∫[-π/2,0](cosθ)^2dθ
主要是d(5sinθ+3)相当于对5sinθ+3求导
那么d(5sinθ+3)=5cosθdθ
∫[-π/2,0]5cosθd(5sinθ+3)=∫[-π/2,0]5cosθ*(5cosθdθ)=25∫[-π/2,0](cosθ)^2dθ
满意请采纳,谢谢~