What about where it's undefined? Well, f prime of x would be undefined. The only place it would be undefined is if you stuck a zero right over here in the denominator, but zero is not in the interval. So the only critical number in the interval is x equals 2. Now we just have to test f at the different endpoints and at the critical number and see which of those is the highest. We're going to test f of 1, which is equal to 8 times the natural log of 1 minus 1 squared. We'll test f of 4, which is equal to 8 times the natural log of 4 minus 4 squared, which is, of course, 16.