Approach #2: Algebra
Take: $x^2 − 7x − 18 = 0$
Factor the left side: $(x - 9)(x + 2) = 0$
So, EITHER $x = 9$ OR $x = -2$

Answer: E


Approach #2: Test each answer choice
(A) −1.
Plug this possible x-value into the equation to get: $(-1)^2 − 7(-1) − 18 = 0$
Simplify: 1 + 7 - 18 = 0. Doesn't work. Eliminate.

(B) 0
Here, we get: $0^2 − 7(0) − 18 = 0$
Simplify: 0 - 0 - 18 = 0. Doesn't work. Eliminate.

(C) 2
Here, we get: $2^2 − 7(2) − 18 = 0$
Simplify: 4 - 14 - 18 = 0. Doesn't work. Eliminate.

(D) 7
Here, we get: $7^2 − 7(7) − 18 = 0$
Simplify: 49 - 49 - 18 = 0. Doesn't work. Eliminate.

(E) 9
Here, we get: $9^2 − 7(9) − 18 = 0$
Simplify: 81 - 63 - 18 = 0. WORKS!

Answer: E