in matlab: Prove that Eq$.(4\mathrm{.}11)$ is exact for all values of x if f$($x$)=$ ax$2+$ bx $+$ c$.$

Eq$.(4\mathrm{.}11)$: f $($xi$+1)\backslash$cong f $($xi $)+$ f $($xi $)$h $+($f$($xi $)/2!)$h$^2$

the Problem qualifies as a proof, not as a Matlab exercise $($if you used Matlab, then it should have only be for supplemental purposes$).$