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April 16, 2014

April 16, 2014

Posted by **carol** on Wednesday, May 4, 2011 at 4:02pm.

x + 4 = -18 => x = -22

or

(x – 7) = -18 => x = -11

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.

- math -
**Reiny**, Wednesday, May 4, 2011 at 6:14pmEric does not understand the concept

It only works if the product is zero

so expand ....

x^2 - 3x - 28 = -18

x^2 - 3x - 10 = 0

(x-5)(x+2) = 0

x = 5 or x = -2

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