So how do I show this? I need the Taylor Series, right? DO I do that for f up to ^2 ? But then what?
>>379961
I think that you just need the definition of derivative and some results on the limes.
Here are some other proof ideas:
https://math.stackexchange.com/questions/1809060/proof-of-the-second-symmetric-derivative
>>379987
Thanks. I think I understand