8.

 

x^2+x-20

When we multiply the first and last coefficients, (1)(-20) = -20

so we are looking for a pair of factors of 20 which have a difference

of 1. There is such a pair, 4 and 5. This gives us the coefficients of the

O and I terms when we recover the FOIL step.

 

x^2-4x+5x-20

 

This will come form

 

 

(x+5)(x-4)