Obviously, anything to the fourth power is always going to be positive. Anything to the second power is always going to be negative. When we do our test, if it's true for positive 3, it's probably going to be true for negative 3 as well. Let's just try it out. When x is just a little bit less than positive 3, what's the sign of f prime prime of x? It's going to be 4 times 9. It's going to be 4 times a positive number.