For which of the following equations are x = 5 and x = –5 both solutions? a. x2 + 25 = 0 b. x2 – 25 = 0 c. x2 + 10x – 25 = 0 d. x2 – 5x – 25 = 0

Short Answer B
Argument
A
A will give you x = +/- 5i 
x^2 + 25 = 0
x^2 = - 25       Take the square root.
sqrt(x^2) = +/- sqrt(-25)
x = +/- (5)i which is a complex number.

B
Is the answer
x^2 = 25
sqrt(x)^2 = sqrt(25)
x = +/- 5

C
Can't be factored just by looking at it. You can show that C is not true just by putting 5 into the equation
f(x) = x^2 + 10x - 25
f(5) = 25 + 10*5 - 25
f(5) = 50
C is not true.

D
D can be eliminated as C was
f(x) = x^2 - 5x - 25
f(5) = -25 ( l'll let you show this is not true). 5 is not a solution because it does not make f(x) = 0