It is better to teach people to fish than to teach them to fish. I'll tell you what to do, and you'll be fine when you encounter this kind of problem in the future. Write the partial derivative of the original function to x, y, then let fx=0 and fy=0 find the values of x, y, and then calculate the second-order partial derivative of the original function, fxx=A, fxy=B, fyy=C, and bring in the newly found values of x, y. If b 2-ac is less than zero, there is an extreme value (otherwise, the extreme value cannot be determined)