∫√(1-x^2)dx
x=sintとする
dx=cost dt

∫(cost)^2*dt
=(1/2)∫(cos2t+1)dt
=(1/4)sin2t+t/2+Ｃ
=(1/4)2sin(t)cos(t)+t/2+Ｃ
=(1/2)｛x√(1-x^2)+
arcsinx｝+Ｃ