Question Number 31511 by abdo imad last updated on 09/Mar/18
$${f}\:{is}\:{C}^{\mathrm{2}} \:{inside}\:{R}\:{and}\:{a}\in{R}\:{find} \\ $$$${lim}_{{h}\rightarrow\mathrm{0}} \:\frac{\left.{fa}+{h}\right)−\mathrm{2}{f}\left({a}\right)\:+{f}\left({a}−{h}\right)}{{h}^{\mathrm{2}} } \\ $$