∫xe^(-x^2)dx|(0,+∞)u=-x^2du=-2xdx∫xe^(-x^2)dx=-(1/2)∫e^udu=-(1/2)e^u+C=-(1/2)e^(-x^2)+C=-1/2e^(x^2)+C∫xe^(-x^2)dx|(0,+∞)=[-1/2e^(+∞^2)+C]-[-1/2e^(0^2)+C]=1/2