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# u-substitution problem (CIE May/June 2012 paper 32) watch

1. I've reached the very end and only problem in my working is that I found not to be the exact same as the answer. I've got -10u du/(3-u)(2+u) but instead it should be positive as the question suggested. I am not sure either with the change in limits whether it's correct, I just found out the method somewhere earlier. Here's my working, please help.

2. (Original post by Taffss)
I've reached the very end and only problem in my working is that I found not to be the exact same as the answer. I've got -10u du/(3-u)(2+u) but instead it should be positive as the question suggested. I am not sure either with the change in limits whether it's correct, I just found out the method somewhere earlier. Here's my working, please help.

When switching the limits you swapped x1 with u2 and x2 with u1 however when doing so you should have put a minus in front of the integral.
3. (Original post by joostan)
When switching the limits you swapped x1 with u2 and x2 with u1 however when doing so you should have put a minus in front of the integral.
I just had that thought and it's confirmed, thaanks it makes sense
4. (Original post by Taffss)
I just had that thought and it's confirmed, thaanks it makes sense
Good

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Updated: April 18, 2013
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