题目
(本题满分10分)计算int e^2xarctansqrt(e^x)-1dx.
(本题满分10分)计算$\int e^{2x}\arctan\sqrt{e^{x}-1}dx$.
题目解答
答案
令 $ t = \sqrt{e^x - 1} $,则 $ e^x = t^2 + 1 $,$ dx = \frac{2t}{t^2 + 1} dt $。代入原积分得:
\[
2 \int t(t^2 + 1) \arctan t \, dt.
\]
分部积分,设 $ u = \arctan t $,$ dv = (t^3 + t) dt $,则:
\[
2 \left[ \left( \frac{t^4}{4} + \frac{t^2}{2} \right) \arctan t - \int \frac{t^4 + 2t^2}{4(1 + t^2)} dt \right].
\]
化简被积函数并积分:
\[
\int \frac{t^4 + 2t^2}{4(1 + t^2)} dt = \frac{1}{4} \int \left( t^2 + 1 - \frac{1}{1 + t^2} \right) dt = \frac{t^3}{12} + \frac{t}{4} - \frac{\arctan t}{4}.
\]
代回并整理得:
\[
\boxed{\frac{e^{2x} + 3}{2} \arctan \sqrt{e^x - 1} - \frac{(e^x - 1)^{3/2}}{6} - \sqrt{e^x - 1} + C.
\]