Help me please with this one, I think it's refers to Mean value theorem, but not sure...
Let us, derivative of a function - is continuous and . Also .
Here goes some hints. Before I solve them for you, try yourself to do it first:-
(i) Define a function
(ii) Find and show that is an increasing function.
(iii) From the criterion for all , get the desired result.
Note: No use of Mean Value Theorem whatsoever.