Natural log derivative problem

[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

 

[saltydog]

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

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.

 

[compute_a_nerd]

Thx so much