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Answer 1 · 2017-11-16T00:18:12

$(x - 5) (x + 4)$ $(x-5)(x+4)$

You need to numbers that add up to the second coefficent (-1) and multiply to get the final constant (-20)

The numbers 4 and -5 work.

So we can rewrite our expression:

$x^{2} + 4 x - 5 x - 20$ $x^2+4x-5x-20$

This is equal to this:

$x (x + 4) - 5 (x + 4)$ $x(x+4)-5(x+4)$

Which is equal to:

$(x - 5) (x + 4)$ $(x-5)(x+4)$