Natural log derivative problem

1. Sep 14, 2005

compute_a_nerd

Hello all. I am stuck on this homework problem. It wants me to find
$$\frac {d^2y} {dx^2}$$
when $$y= ln x^8$$
The book answer is $$\frac {-8}{x^2}$$
But I only can get $$\frac {-8}{x^9)}$$

Please give me some guidance
Thanks

Last edited: Sep 14, 2005
2. Sep 14, 2005

saltydog

Need to keep very clear the precedence of operators so write it as:

$$y=ln(x^8)$$

Now, just differentiate once to get 8/x, one more time to get the book's answer.

3. Sep 14, 2005

compute_a_nerd

Thx so much

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