# Why can't you use substitution to integrate ln(2x+1)?

**URL:** <https://forum.kirupa.com/t/why-cant-you-use-substitution-to-integrate-ln-2x-1/180717>\
**Category:** random\
**Created:** [March 3, 2006, 12:31am UTC](https://forum.kirupa.com/t/why-cant-you-use-substitution-to-integrate-ln-2x-1/180717 "2006-03-03T00:31:04Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![MTsoul](https://avatars.discourse-cdn.com/v4/letter/m/91b2a8/32.png) [@MTsoul](https://forum.kirupa.com/u/MTsoul)\
**Post date:** [March 3, 2006, 12:31am UTC](https://forum.kirupa.com/t/why-cant-you-use-substitution-to-integrate-ln-2x-1/180717/1 "2006-03-03T00:31:04Z")

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I’m learning integration by parts, and came across the question:

integrate ln(2x+1)dx (I can’t do the integral sign, but you get the idea).

I did it with integration by parts, but when I do it with substitution, it doesn’t work (not the right answer). Why can’t I just substitute 2x+1 by u and integrate ln(u) and substitute 2x+1 back in later?