Problem 730 (difficulty: 6/10)

Is it true that if \(\displaystyle f\) is 2 times differentiable at \(\displaystyle a\), then

\(\displaystyle \lim_{h\to 0}\frac{f(a+2h)-2f(a+h)+f(a)}{h^2} = f''(a)\ ?\)

Hint-->

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