Question

Where is my mistake?

Answer 1

This is problem 7, page 97.
Find derivative of\[\frac{1}{(3x+1)^4}\]
If I rewrite to
\[(3x+1)^{-4}\]
Then using the chain rule I get
\[-4(3x+1)^{-5}(3)=\frac{-12}{(3x+1)^5}\]
Which is the correct answer.

However, if I try to use the quotient rule then I get a different answer, and right now I can't see what I'm doing wrong.

\[\frac{(3x+1)^4(0)-4(3x+1)^3(3)(1)}{(3x+1)^5}=\frac{-12(3x+1)^3}{(3x+1)^5}=\frac{-12}{(3x+1)^2}\]
I'm sure it is some silly mistake that I just can't spot right now

Answer 2

You did not square your function in the denominator.

Answer 3

ahh - of course - thank you. I knew it was getting too late