3 ms·∫0->∞ x*e^-tx dx = -∂_t ∫0->∞ e^-tx dx = -∂_t (1/t)∫0->∞ e^-u du = -∂_t (1/t) = 1/t^2by greens 6y ago∫0->∞ x*e^-tx dx = -∂_t ∫0->∞ e^-tx dx = -∂_t (1/t)∫0->∞ e^-u du = -∂_t (1/t) = 1/t^2