∫x^3/√(1+x^2)dx=1/2∫x^2/√(1+x^2)dx^2=1/2∫(x^2+1-1)/√(1+x^2)dx^2=1/2∫[√(1+x^2)-1/√(1+x^2)]dx^2=1/3(1+x^2)^(3/2)-√(1+x^2)+C
