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# Integration by substitution watch

1. Let , so
when ,
when ,

therefore

The answer is - where have I gone wrong?

2. (Original post by whatacrydonnie)

Let , so
when ,
when ,

therefore

The answer is - where have I gone wrong?

Having eliminated the lower limit of zero, both u^(5/2) and u^(3/2) equal 1. that gets you 2(1)/5 + 4(1)/3 which is the same as 6/15 + 20/15 = 26/15.

Edit: In case more clarification is needed, you seem to have multiplied 1 by the preceding number (2 and 4) and then exponentiated the result, rather than dealing with the exponentiation first.
3. (Original post by whatacrydonnie)

Let , so
when ,
when ,

therefore

The answer is - where have I gone wrong?

You have done 2times u before applying the power

The power is only applied to the u

0 to a power is 0
1 to a power is 1
4. (Original post by The Financier)
Having eliminated the lower limit of zero, both u^(5/2) and u^(3/2) equal 1. that gets you 2(1)/5 + 4(1)/3 which is the same as 6/15 + 20/15 = 26/15.

Edit: In case more clarification is needed, you seem to have multiplied 1 by the preceding number (2 and 4) and then exponentiated the result, rather than dealing with the exponentiation first.
(Original post by TenOfThem)
You have done 2times u before applying the power

The power is only applied to the u

0 to a power is 0
1 to a power is 1
Thanks, both of you!
I knew I'd made a stupid mistake, I just couldn't see it

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