The Student Room Group

Integration by substitution

How would I Integrate this expression ?
http://imgur.com/6Ve5GQd


I tried to make u= 2x +1 But I get stuck with
(ln u)/ (squareroot u) at the end
Reply 1
Original post by jon2016
How would I Integrate this expression ?
http://imgur.com/6Ve5GQd


I tried to make u= 2x +1 But I get stuck with
(ln u)/ (squareroot u) at the end


Have you tried IBP with u = ln x and v = 1/sqrt(x)?
Reply 2
The substitution u=2x+1 u=\sqrt{2x+1} works really nicely here.
Reply 3
Original post by B_9710
The substitution u=2x+1 u=\sqrt{2x+1} works really nicely here.

Would you mind showing your working out ? Think im having a brain freeze
Reply 4
Original post by Zacken
Have you tried IBP with u = ln x and v = 1/sqrt(x)?

ah didnt occur to me to combine the two methods
I have attempted it but it got sort of messy, could I see your working out ?
Reply 5
Original post by jon2016
Would you mind showing your working out ? Think im having a brain freeze


It comes out to lnu du \int \ln u \ du which should tell you something about the derivative of ln2x+1 \ln{ \sqrt{2x+1}} .
Reply 6
Original post by B_9710
It comes out to lnu du \int \ln u \ du which should tell you something about the derivative of ln2x+1 \ln{ \sqrt{2x+1}} .


when you differentiate
Unparseable latex formula:

u = \ \sqrt{2x+1}}



you get
du = (2x+1)^-1/2 dx right ?

Then du/ (2x+1)^-1/2 = dxso you can now replace dx in the original expression with the above.So I have Ln(2x+1)/u * du/ (2x+1)^-1/2
(edited 7 years ago)
Original post by jon2016
when you differentiate
Unparseable latex formula:

u = \ \sqrt{2x+1}}



you get
du = (2x+1)^-1/2 dx right ?


Yes.
Reply 8
Original post by B_9710
It comes out to lnu du \int \ln u \ du which should tell you something about the derivative of ln2x+1 \ln{ \sqrt{2x+1}} .


what would be the final answer ?
Reply 9
Original post by jon2016
what would be the final answer ?


Use IBP with u = ln x and dv = 1

Quick Reply

Latest