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# integration by substitution watch

1. How on earth do i start this , can someone please explain me bit more about substitution integration.
I seem to have got basic idea of it but i dont get the right answers =/

=/ well i started off by first differentiating u= 4x+1
=> du/dx = 4 , du= 4dx , dx= 1/4du
now this is where i screw up , i think =/
before Integration:
2x / (4x+1)^2
=> after: x^2 (-u)^-1 x1/4 du (where i believe du becomes constant ?)
2. (Original post by ibysaiyan)
How on earth do i start this , can someone please explain me bit more about substitution integration.
I seem to have got basic idea of it but i dont get the right answers =/

=/ well i started off by first differentiating u= 4x+1
=> du/dx = 4 , du= 4dx , dx= 1/4du
now this is where i screw up , i think =/
before Integration:
2x / (4x+1)^2
=> after: x^2 (-u)^-1 x1/4 du (where i believe du becomes constant ?)
your use of notation makes it very difficult to follow what you are doing.
Anyway, just replace all instances of x in the original equation with the proposed substitution , simplify and integrate.

there should not be any "x's" once you have made your substitutions ....
3. Sorry about my lack of latex skill =/ , but i still dont get it. what you mean is that i need to replace all the "x's" into (4x+1)?
4. OHHH! I think i get it now thanks alot , i wasn't subbing in x values ^^ oh nvm
5. (Original post by ibysaiyan)
Sorry about my lack of latex skill =/ , but i still dont get it. what you mean is that i need to replace all the "x's" into (4x+1)?
eh?

I'm sorry, but I really am struggling to understand what you mean.

you suggested using the substitution u=4x+1

well x=(u-1)/4 ........ so use it !!
6. (Original post by Mrm.)
eh?

I'm sorry, but I really am struggling to understand what you mean.

you suggested using the substitution u=4x+1

well x=(u-1)/4 ........ so use it !!
Roger that. lol seems i cant multi-task .

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