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#1 Help Me ! » Substitution u = x^3 » 2008-08-27 11:10:07

boneill3
Replies: 1

Hi Guys,
I've been asked to substitute u = x^3 in the following integral int x^2/ (1+x^6)

Do I substitute by   int x^2/(u^3) and have a scaler out the front?

or do I start by having int u^-1 / 1+ u^3.

Any help to point me in the right direction would be greatly appreciated.
regards
Brendan

#2 Re: Help Me ! » Integration by substitution » 2008-08-19 08:10:51

Hi Guys Thankyou for your replies.
Do you always solve for X if the derivative of the inner function (3x + 8 ) is not the exactly the first function ie x
once again thank you.
regards
Brendan

#3 Help Me ! » Integration by substitution » 2008-08-17 14:55:45

boneill3
Replies: 5

Hi Guys,
Im working on an integration problem using substitution and wondering if I'm doing it right.
Can some one please Have a look and see how i'm going?


The problem is int x sqrt 3*x+8

first I let u = 3*x + 8  which makes du/dx = 3

I than integrate  int   sqrt u     = int u^1/2


= 1/3 int 2/3 (u^3/2) + C


=1/3 (2/3(3*x+8)^3/2 + C)

Is this right?
regards
Brendan

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