SAT Math Question of the Day

Q: If (3 - a)(3 + a) = -7, then what is a possible value for a?

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

UNANSWERED.

The correct answer is B.

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 A, where a is -5,
(3 - a)(3 + a) = -7
(3 - -5)(3 + -5) = -7
(8)(-2) = -7
-16 = -7
Nope, choice A doesn't work. On to choice B: a is -4 ...
(3 - a)(3 + a) = -7
(3 - -4)(3 + -4) = -7
(7)(-1) = -7
-7 = -7
IT WORKS!
So the answer is a is -4 or choice B.

Another way to solve it is algebraically:
(3 - a)(3 + a) = -7
(a - 3)(a + 3) = 7
a² - 9 = 7
a² = 16
a = 4 or -4
So, B is the correct answer.