Question

How do you use the chain rule to differentiate `f(x) = cos(lnx)`?

Answer 1

Let `y = cosu` and `u = lnx`.

Then `y' = -sinu` and `u' = 1/x`

`f'(x) = -sinu xx 1/x = -sin(lnx) xx 1/x = -(sin(lnx))/x`

Hopefully this helps!