(x-a)(x-b) is equal to x^2-xb-ax-ab= x^2 -x(b+a) –ab or = x^2 -b(x+a) –ax.

The x minus a and b takes the quadratic formula and includes steps that should govern with above formula by operating and come across in an identify of same sort.

This is binomial expansion of the form and each of these terms can be resultant value.