Divide both sides by 4, you get 1 fourth is equal to x squared. And then what x values is this true at? Well, we just take the plus or minus square root of both sides and you get x is equal to plus or minus 1 half. Negative 1 half squared is 1 fourth, positive 1 half squared is 1 fourth. So at x equals plus or minus 1 half, f prime or the derivative is equal to 0. So let me write it this way. f prime of 1 half is equal to 0, and you can verify that right over here.