Hi. For a two-variable function, at point Z all first-partials are zero, all second-order-partials are zero, but fxxx (third-order-partial) is non-zero. Is Z is local minimum, maximum, or neither?
I can't use the second derivative test because it's 0 which is inconclusive.
I think it could either be a minimum or maximum. But I don't know why... (Headbang)