You get 3x squared is equal to 12. Divide both sides by 3. You get x squared is equal to 4. Well, this is going to happen when x is equal to 2 and x is equal to negative 2. Just to be clear, f prime of 2, you get 3 times 4 minus 12, which is equal to 0. And f prime of negative 2 is also, same exact reason, is also equal to 0. So we can say, and I'll switch colors here, that f has critical points at x equals 2 and x equals negative 2.