x=sina
a=arcsinx
cosa=√(1-x²)
所以sin2a=2sinacosa=2x√(1-x²)
√(1-x²)=cosa
dx=cosada
原式=∫sin²a*cosada/cosa
=∫sin²ada
=∫(1+cos2a)/2da
=1/4*∫(1+cos2a)d2a
=1/4*(2a+sin2a)+C
=1/4[2arcsinx+2x√(1-x²)]+C