If it's not zero, then it's neither. And then if it is zero, if we want to figure out relative minimum or relative maximum, we can evaluate the sign of the second derivative. So let's just think about this. So we want to evaluate f prime, we want to figure out what f prime of, f prime of two is equal to. So we know that f prime of x, f prime of x, which is the same thing as dy, dx, is equal to two times x minus y. We saw that in the last problem. And so f prime of two, right this way, f prime of two is going to be equal to two times two, two times two, minus whatever y is when x is equal to two.