SOLUTION: In solving the equation (x + 4)(x – 4) = 9, Eric stated that the solution would be x + 4 = 9 => x = 5 or (x – 4) = 9 => x = 13 However, at least one of these solutions fails to

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: In solving the equation (x + 4)(x – 4) = 9, Eric stated that the solution would be x + 4 = 9 => x = 5 or (x – 4) = 9 => x = 13 However, at least one of these solutions fails to      Log On


   

Question 665588: In solving the equation (x + 4)(x – 4) = 9, Eric stated that the solution would be
x + 4 = 9 => x = 5
or
(x – 4) = 9 => x = 13
However, at least one of these solutions fails to work when substituted back into the original equation. Why is that? Please help Eric to understand better; solve the problem yourself, and explain your reasoning.
please help me!
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

The Idea is   (x + 4)(x – 4) = 9    needs to be set to ZERO to solve for x.

 (x + 4)(x – 4) = 9

x^2 - 16 = 9

  x^2 - 25 = 0    || Now it is in a format to solve for x

 (x-5)(x+5) = 0

 (x-5) = 0,  x = 5

0r (x+5) = 0, x = -5