题目
已知 f(x)=int_(1)^x e^t^(2) dt,则 int_(0)^1 f(x) dx= _________.
已知 $f(x)=\int_{1}^{x} e^{t^{2}} dt$,则 $\int_{0}^{1} f(x) dx=$ _________.
题目解答
答案
设 $ f(x) = \int_{1}^{x} e^{t^2} \, dt $,则 $ f'(x) = e^{x^2} $。
利用分部积分法,令 $ u = f(x) $,$ dv = dx $,则 $ du = f'(x) \, dx $,$ v = x $。
$\int_{0}^{1} f(x) \, dx = \left[ x f(x) \right]_{0}^{1} - \int_{0}^{1} x f'(x) \, dx$
由于 $ f(1) = 0 $,故 $ \left[ x f(x) \right]_{0}^{1} = 0 $,积分简化为:
$\int_{0}^{1} f(x) \, dx = - \int_{0}^{1} x e^{x^2} \, dx$
令 $ u = x^2 $,则 $ du = 2x \, dx $,当 $ x = 0 $ 时 $ u = 0 $,当 $ x = 1 $ 时 $ u = 1 $,代入得:
$\int_{0}^{1} x e^{x^2} \, dx = \frac{1}{2} \int_{0}^{1} e^u \, du = \frac{1}{2} (e - 1)$
因此,原积分值为:
$\int_{0}^{1} f(x) \, dx = -\frac{1}{2} (e - 1) = \frac{1 - e}{2}$
答案: $\boxed{\frac{1 - e}{2}}$