2 7*x - 28
7*x^2 - 1*28
1*(x + 2)*(x - 2)
(1*(x + 2))*(x - 2)
-28.0 + 7.0*x^2
/ 2\ 7*\-4 + x /
7*(-4 + x^2)
7*(-2 + x)*(2 + x)