变限积分函数的性质主要由被积分函数的性质、积分上(下)限的结构来决定。

The variation range integral function nature mainly by the structure which by in the integral function nature, the integral (next) is limited decided.

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通常，你只会在这两种情况下用替代法，或者这可以极大地简化被积函数，或者就是这可以简化，积分的上下限。

I mean, normally, you would only do this kind of substitution if either it simplifies a lot the function you are integrating, or it simplifies a lot the region on which you are integrating.

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采用将圆电流磁矢势表达式中一部分展成级数，使被积函数变成可积分的函数。

A part of results on magnetic vector potential of circular loop are expanded, so the integral function is transformed to integrable series.

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