Hi there. I've got some doubts about the maxima and minima on this function: . I've looked for critical points, and theres only one at (0,0). The thing is that when I've evaluate the second derivatives I've found that , then I have not a defined criteria on this case, cause the criteria that I have defines the concavity for and . I don't know what happens when . I think the criteria fails, but I don't actually know what to do.