分子是 (u^2)' = 2uu', 其中 u = ∫<0, x>e^(t^2)dt则 (u^2)' = 2 [∫<0, x>e^(t^2)dt] e^(x^2) = 2e^(x^2)∫<0, x>e^(t^2)dt
