( X+ a)( X+b) = X^{2} + ( a+b)X+^{ }ab
This is a general formula, where Multiplying binomial by binomial result in a trinomial( polynomial of 2nd degree or quadratic).
You have to be able to factor any quadratic 2 two binomial, and solve it.
and expand it.
( X1) ( X +30) = X^{2 }+ 29X  30
( X  5) ( X +6 ) = X^{2 }+ X 30
( X + 2) ( X 15) = X^{2}  13X  30 You see that Coeficient of X is ( a+b) and constant is ab
Sep 4

Parviz F.