plese can you help me to solve this problem? thank you:

Let be x1,...xn a random sample from random variable X with f (x/r) (pdf) to which the regularity conditions are satisfied. If m is a estimator unbiased to g(r). to show that

variance(m)>= (((g(r))^2)/(nE((d (logf(x/r))/dr)^2)