# Homework Help: Derivitive with ln - don't understand

1. Mar 11, 2009

### zeion

1. The problem statement, all variables and given/known data

Differentiate the following:
y = ln(2x^2 - 2) / x^2 - 1

3. The attempt at a solution

The answer is y' = -ln(2x^2 - 2)(2x)(x^2 - 1)^-2 + 4x / 2x^2 - 2 (x^2 - 1)^-1

I understand all of it except 4x / 2x^2 - 2, how does ln(2x^2 - 2) derive into 4x / 2x^2 - 2?

2. Mar 11, 2009

### rock.freak667

$$\frac{d}{dx}(ln(f(x))=\frac{f'(x)}{f(x)}$$

3. Mar 11, 2009

### zeion

Oh okay, thanks, never seen that one before.

4. Mar 11, 2009

### Hurkyl

Staff Emeritus
If you look closely, you'll notice that's just the chain rule....

5. Mar 11, 2009

### zeion

Really? How?

6. Mar 11, 2009

### mblack

To see how it is the chain rule, think about what the derivative of ln x is.