How do you factor the expression #x^2 - 13x + 40#?
There are many ways to factor. One method I like to use is the diamond method when you try to find the two numbers that add up to b and multiply to ac.
So you want to find two numbers that add up to -13 and multiply to 40. You can find the factors of 40 and find the pair that adds up to -13. -8 and -5 multiply to 40 and add up to -13.
You can use foil to test it