# 2 Integration questions.

1. May 2, 2007

### Joza

I need help on these two integration questions:

1.

(x^2 -16)/(2x + 8) dx

2.

1/(1+9x^2) dx

I can't seem to find a "u" for either. And I tried a tan identity on number 2 to no avail.

2. May 2, 2007

### Office_Shredder

Staff Emeritus
Did you try factoring the first one?

3. May 2, 2007

### Joza

OH WAIT.....

Yea so x^2 - 16 would be (x + 4)(x - 4).

Then I can pull a 1/2 outside, and I'll be left with (x + 4) on the bottom. That will cancel out, so it will be the integral of (x - 4)???

4. May 2, 2007

### HallsofIvy

Staff Emeritus
Well, because of that 1/2 you "pulled outside", it will be (1/2) the integral of x-4.

As far as the second is concerned, you might try letting u= 3x and then think about the derivative of arctan u.

5. May 2, 2007

### Joza

Yea thats what I meant.

Well I tried using 1/(1^2 + (3x)^2).....but that didnt work.

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