How do you solve x^2+x-20=0 by factoring?

Aug 7, 2015

You have to find two factors of $20$ with a difference of $1$ (since the $20$ has a $-$sign.

Explanation:

You can try $1 \cdot 20 , 2 \cdot 10 \mathmr{and} 4 \cdot 5$
$4 \cdot 5$ gives a difference of $1$
They have to be opposite signs, and add up to $+ 1$

So the factoring goes like:
$\left(x + 5\right) \left(x - 4\right) = 0 \to x = - 5 \mathmr{and} x = + 4$