May 4th, 2017, 11:27 AM  #21  
Senior Member Joined: Jun 2015 From: England Posts: 915 Thanks: 271  Quote:
 
May 4th, 2017, 12:03 PM  #22 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,675 Thanks: 2655 Math Focus: Mainly analysis and algebra  Pick a better $u(x)$ or be very careful when converting back from $u$ to $x$. The only place I've seen it matter is in trigonometric substitutions where there is always another option. The problem arises because in going from $u$ to $x$ we need the inverse function $u^{1}$, but this is not well defined if $u$ is not monotonic. You may have to make sure that you are picking the correct value for $x$. 

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calculus, indefinite, indefinite integrals, integrals 
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