SAT Math Question of the Day

Q: If (x - 3)(x + 3) = 16, then what is a possible answer for x?

1. 1
2. 2
3. 3
4. 4
5. 5

UNANSWERED.

The correct answer is E.

A:

One way to do this problem is to just plug in the possible answers and see which one fits the equation.

Let's try choice C, where x is 3, first:
(x - 3)(x + 3) = 16
(3 - 3)(3 + 3) = 9
(0)(6) = 9
0 = 9
Opps, our number is too small. Let's try a larger x=5.

Let's try choice E, where x is 5:
(x - 3)(x + 3) = 16
(5 - 3)(5 + 3) = 16
(2)(8) = 16
16 = 16
IT WORKS!
So the answer is x is 5 or choice E.

Another way to solve it is algebraically:
(x - 3)(x + 3) = 16
x² - 9 = 16
x² = 25
x = 5 or -5
So, E is the correct answer.