Stuck on Natural Log Derivative Problem?

[compute_a_nerd]

Hello all. I am stuck on this homework problem. It wants me to find
<br /> \frac {d^2y} {dx^2} <br />
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
<br /> \frac {d^2y} {dx^2} <br />
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