请问这个题怎么证明的?麻烦附带说明一下理由,

把h看成自变量,使用两次洛比达法则
lim [f(x0+h) + f(x0-h) - 2f(x0)] / h^2
= lim [f'(x0+h) - f'(x0-h)] / (2h)
= lim [f''(x0+h) + f''(x0-h)] / 2
= f''(x0)