Whenever a number is squared, it will always be positive. So since you have -4^2 up there, it will equal the exact same as 4^2 does, which is plainly the positive number 16. This is because a negative multiplied by one other negative is always a positive (-4*-4 = 16). So for every expression you've got, -4^2, (-4)^2, and 4^2, they all have positive simplified results.