>>566
∫(a^2-x^2)^1/2dx=x(a^2-x^2)^1/2-∫x{(a^2-x^2)^1/2}'dx
=x(a^2-x^2)^1/2-∫(1/2)(-2x)*x(a^2-x^2)^(-1/2)dx
=x(a^2-x^2)^1/2+∫x^2(a^2-x^2)^(-1/2)dx
=x(a^2-x^2)^1/2+∫(x^2-a^2)(a^2-x^2)^(-1/2)dx+a^2∫(a^2-x^2)^(-1/2) dx
=x(a^2-x^2)^1/2-∫(a^2-x^2)^(1/2)dx+a^2∫1/(a^2-x^2)^(1/2) dx