SAT Math Question of the Day

Q: If (x - 5)(5 + x) = -9, then what is a possible answer for x?

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

UNANSWERED.

The correct answer is D.

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 - 5)(5 + x) = -9
(3 - 5)(5 + 3) = -9
(-2)(8) = -9
-16 = -9
Opps, our result is too small. Let's try a x=4

Let's try choice D, where x is 4:
(x - 5)(5 + x) = -9
(4 - 5)(5 + 4) = -9
(-1)(9) = -9
-9 = -9
IT WORKS!
So the answer is x is 4 or choice D.

Another way to solve it is algebraically:
(x - 5)(5 + x) = -9
(x - 5)(x + 5) = -9
x² - 25 = -9
x² = 16
x = 4 or -4
So, D is the correct answer.