※ 引述《a224996 (绿茶)》之铭言： : 1. ∫xlnx dx : 2. ∫x/1+x^2 dx 上下极限 正负无穷大 : 请帮解... 1. 分部积分 ∫xlnx dx = (1/2)x^2lnx - ∫(1/2)x dx = (1/2)x^2lnx - (1/4)x^2 + c 2. 令 t = 1 + x^2 => dt = 2xdx => xdx = (1/2)dt => ∫(1/2)(1/t)dt = (1/2)ln|t| = (1/2)ln|1+x^2| 发散?? --

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