Remember, that's just the numerator of our second derivative. Any x that makes the numerator 0 is making the second derivative 0. So let's factor out a 4x squared. Now we'll have 27 times, if we factor a 4 out of the 12, we'll just get a 3, and we factored out the x squared, minus, we factored out the 4, we factored out an x squared, so we have x to the 4th is equal to 0. So the x's that will make this equal to 0 will satisfy either 4x squared is equal to 0, or, now 27 times 3, I can do that in my head, that's 81, 20 times 3 is 60, 7 times 3 is 21, 60 plus 21 is 81. Or 81 minus x to the 4th is equal to 0. Any x that satisfies either of these will make this entire expression equal to 0, so if this thing is 0, the whole thing is going to be equal to 0.