Prove that second partial derivatives are not equal
math.stackexchange.com › questions › 3253340Jun 06, 2019 · If I find second partial derivatives at $(x,y) e(0,0)$, I'll get total equality because both of them are continuous. If I find either first partial derivative at $(0,0)$, I'll get $0$. It seems to me that, therefore, second partial derivatives at $(0,0)$ will be zeros too. So, what am I doing wrong?
Symmetry of second derivatives - Wikipedia
https://en.wikipedia.org/wiki/Symmetry_of_second_derivativesThe result on the equality of mixed partial derivatives under certain conditions has a long history. The list of unsuccessful proposed proofs started with Euler's, published in 1740, although already in 1721 Bernoulli had implicitly assumed the result with no formal justification. Clairaut also published a proposed proof in 1740, with no other attempts until the end of the 18th century. Starting then, for a period of 70 years, a number of incomplete proofs were proposed. The proof of