# Math Help - Algebra problem

1. ## Algebra problem

It says solve by factoring--- x^2 + 2x = 15 I know the answer is x=3 or -5, but I have no idea how to get there by factoring. Any help would be very much appreciated since on the test we will have to show our work.

2. Originally Posted by onetreehill56
It says solve by factoring--- x^2 + 2x = 15 I know the answer is x=3 or -5, but I have no idea how to get there by factoring. Any help would be very much appreciated since on the test we will have to show our work.
$x^2 + 2x - 15 = 0$

List the pairs of factors of -15:
1, -15
3, -5
5, -3
15, -1

Which of these add to 2? 5 + (-3) = 2. So
$x^2 + 2x - 15 = 0$

$x^2 + 5x - 3x - 15 = 0$

$(x^2 + 5x) + (-3x - 15) = 0$

$x(x + 5) - 3(x + 5) = 0$

$(x - 3)(x + 5) = 0$

-Dan

3. ## Factored

x^2+2*x-15=0 can be factored into (x+5)*(x-3)