http://img.photobucket.com/albums/v2...5/Untitled.jpg

http://upload.wikimedia.org/math/9/a...4da75f5d99.png

I tried to write out the taylor's theorem formula , but from there onwards i have no idea how to continue to show $\displaystyle 1\leq f(\frac{1}{2}) \leq \frac{5}{4}$

Can anyone guide me along? Thanks in advance. (Nod)