Assume f(x) is differentiable at e. Prove that if f(x)>0, then f(ek)<f(e)<f(e+k) for all positive k sufficiently small.

Problem: 

Assume f(x) is differentiable at e. Prove that if f(x)>0, then f(ek)<f(e)<f(e+k) for all positive k below some sufficiently small value.

Answer: 

It is true that if f(x)>0, then f(ek)<f(e)<f(e+k) for all positive k below some sufficiently small value.