∫1到+∞ 1/2*x*e^(x-1)*dx=∫1到+∞ 1/2*xde^(x-1)= 1/2*x*e^(x-1)|1到+∞-∫1到+∞ 1/2e^(x-1)*dx=1/2*x*e^(x-1)|1到+∞-1/2e^(x-1)|1到+∞=1/2(*x-1)e^(x-1)|1到+∞=+∞
