Simplify x^2 - 9x + 20

Firstly write out the equation x² - 9x + 20 = 0. The aim is to find two numbers that multiply to make 20 and add up to make -9. Look at the constant without any x's , in this case it is 20. We need to work out the combination of factors for 20. The factors are 1 and 20, 2 and 10, 4 and 5. We now look at the -9x in the equation. Look at the combinations of factors and see which ones total to make -9. In this case it is 4 and 5. However, you will need -4 and -5 as the 9 is a negative. This works as -4 x -5 = 20 and -4 + -5 = -9. The simplified equation is therefore (x-4)(x-5).