2 x + x - 20
x^2 + x - 20 при x = -1
x^2 + x - 20
(-1)^2 + (-1) - 20
(-1)^2 - 1 - 20
-20
-20.0 + x + x^2
-20 + x*(1 + x)
(-4 + x)*(5 + x)