Need Help

on the internet i found the following epsilon delta generic limit proof

f(x) = Ax^2 + Bx +C as limit of x approaches p

Delta = Min 1 or E/ /a/ +/2ap+b/

A=3 B=4 C=5 P=2-----------------How did they come up with the part E divided by /a/ + /2ap+B/

They continued and proved the limit but i cannot see how they got the E divided by the constants first.

Could someone show me the algebra or the reasoning on how they got the bound this way.

Thank You

Del