If there are two unique solutions to the equation x^2 + bx + 9 = 0, which of the following could not be a value of b?

[BTGmoderatorDC]

If there are two unique solutions to the equation x^2 + bx + 9 = 0, which of the following could not be a value of b?

A. -10
B. -6.5
C. -6
D. 6.5
E. 10


OA C

Source: Veritas Prep

[Scott@TargetTestPrep]

If there are two unique solutions to the equation x^2 + bx + 9 = 0, which of the following could not be a value of b?

A. -10
B. -6.5
C. -6
D. 6.5
E. 10


OA C

Solution:

Looking at our answer choices, we see that b cannot be -6. If b were -6 we would have:



x^2 - 6x + 9 = 0

(x - 3)(x - 3) = 0
x - 3 = 0 → x = 3

As we can see, if b = -6, there would be only one unique solution. However, since there must be two unique solutions, -6 can’t be a possible value for b.

Answer: C