先計算不定積分∫√(x/(1-x))dx
令√x=sint,√(1-x)=cost,x=(sint)^2,dx=2sintcostdt
原式=∫ sint/cost*2sintcostdt
=2∫ (sint)^2dt
=∫ (1-cos2t)dt
=t-(1/2)sin2t+C
=t-sintcost+C
=arcsin√x-√x*√(1-x)+C
=arcsin√x-√(x-x^2)+C
代值進去=π/2