Question

How do you factor the trinomial `x^2 - 9x + 20`?

Answer 1

You try to find two numbers that add up to `-9` and multiply to `+20`

Explanation:

You can first factor `20`
`20=+-1*+-20=+-2*+-10=+-4*+-5`

Since the sign of `20` is positive, both factors must have the same sign. Since the sign of `9` is negative, they must both be negative.
Only answer is `-4and-5`

So the factoring goes:
`=(x-4)(x-5)`