. In solving the equation (x + 4)(x – 7) = -18, Eric stated that the solution would be
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?

Question

. In solving the equation (x + 4)(x – 7) = -18, Eric stated that the solution would be
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?

hero · Answer

Eric solved the problem incorrectly

anonymous · Answer

oh dear you can't do that, you have to get 0 on one side of the equation

anonymous · Answer

hero do you want to take this one?

hero · Answer

He should multiply the binomials together first, then add 18 to both sides. Then solve for x

hero · Answer

Eric should do this: 

(x + 4)(x – 7) = -18
x^2 - 3x - 28 = -18
x^2 - 3x - 10 = 0
x^2 - 5x + 2x -10 = 0
x(x-5)+2(x-5) = 0
(x-5)(x-2) = 0
x =2,5

anonymous · Answer

yup! I concur