# Homework Help: Integrals using log rule

1. May 6, 2010

### fluxions22

1. The problem statement, all variables and given/known data
integral of x/square root of 9- x^2

2. Relevant equations

1/x dx= ln |x| + c

3. The attempt at a solution
3 ln|x| + c

2. May 6, 2010

### vela

Staff Emeritus
You need to show more work. At this point, it looks like you're just guessing.

So you have the integral

$$I=\int \frac{x}{\sqrt{9-x^2}}\,dx$$

right? I don't see how

$$\int \frac{dx}{x} = \ln |x| + c$$

applies at all.

3. May 6, 2010

### physicsman2

Try factoring out a 9 in the denominator in the square root. It should be somewhat obvious from there what you need to do.

4. May 6, 2010

### Staff: Mentor

A simpler approach is to use an ordinary substitution. Using this approach you don't need to factor anything out of the radical.

5. May 6, 2010

### physicsman2

Oh whoops, I didn't see the x in the numerator. I thought there was only a 1 in the numerator, which is why I thought that at first. You're right.