Consider ln[f(x)]. By using ln(a/b)=ln(a)-ln(b) and ln(ab)=ln(a)+ln(b) you can break ln[f(x)] down into a bunch of smaller terms. Now differentiate each term implicitly and remember (ln(y)) ' = (1/lny) * y'. Gather up all the y' terms and eventually you'll get your answer. Good luck.