Factorise: a squared -9a + 20? what are all the steps?

A² - 9a + 20

Factorization!

The sum is: -9
and the product is: 20

Since the sum is negative, the numbers that gave the outcome will be negative because the product is positive as well.

What and what adds to gives us -9?
What and what multiplies to give us 20?
-10 + 1 gives us -9
But the product will be -10 × 1 = -10 (its incorrect)

-4 - 5 = -9
(-4) × (-5) = 20

These satisfy both the sum and the product.

The expression will be:
(a - 4)(a - 5)

Why are u not just putting the numbers this is to much