Hi,

f(r) = [V * ln(r/b)] / ln(a/b)

Differentiating, I get:

f'(r) = V/[r * ln(a/b)]

But my notes say:

f'(r) = V/[r * ln(b/a)]

The difference is in my answer there is ln(b/a), but in my notes it has ln(a/b). Which is right, and why?

Thanks

Edit: The notes then multiply f'(r) by -1, making the answer in the notes correct.