Respuesta :
You have to use the distributive property:
(x*x)+(x*5)+(-4*x)+(-4*5)
x^2+5x-4x-20
x^2+x-20
(x*x)+(x*5)+(-4*x)+(-4*5)
x^2+5x-4x-20
x^2+x-20
(x-4)(x+5)
x^2+5x-4x-20 (Step one: FOIL)
x^2+x-20 (Step two: Combine like terms)
x^2+5x-4x-20 (Step one: FOIL)
x^2+x-20 (Step two: Combine like terms)