# Homework Help: Help with integral

1. Jun 10, 2015

### ArmandStarks

1. The problem statement, all variables and given/known data
The problem is this:
∫[√x /(1+x)] dx
I used sustitution method
u= √x
u^2=x
2udu=dx

2. Relevant equations
My new integral is:
∫[(u*2udu)/(1+u^2)]du
2∫[u^2/(1+u^2)]du
I need help to reduce this point to continue, I guess I need some algebraic steps

3. The attempt at a solution

The book shows: x^3/3 -3x - 10Ln|x-5| + C as the answer but I think this is wrong because I don't have x-5 anywhere

2. Jun 10, 2015

### Staff: Mentor

This looks OK. I would use polynomial long division to turn this improper rational expression into a nicer form for integration. If you're not familiar with this technique, do a web search for "polynomial long division".
I agree - the book's answer doesn't look right.

3. Jun 10, 2015

### SammyS

Staff Emeritus
Hello ArmandStarks. Welcome to PF !

You can use "long division" to divide u2 by (u2 + 1) .

Or use the following "trick" .

$\displaystyle \frac{u^2}{1+u^2}=\frac{u^2+1-1}{1+u^2}$

$\displaystyle =\frac{1+u^2}{1+u^2}-\frac{1}{1+u^2}$​

4. Jun 10, 2015

### ArmandStarks

I just found that "trick" and the 2 integrals are easy to do.
Thank you both!

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