Find the derivative of f(x)=[lnx]^4

Answer 1

let z = ln x
dz = dx/x
dx = x dz
then
f(z) = z^4
df = 4 z^3 dz = 4 z^3 dx/x
df/dx = (4 /x) (ln x)^3

Answer 2

Thank you! I've been stuck on that problem all night.