Question 165978
(a+b) (a-b) is a special set of factors when multiplied together because two of the terms are cancelled out so you end up with {{{a^2-b^2}}} also called the difference of two squares. In other words any time you have the sum of two variables multiplied by the difference of those variables you end up with this pattern.  When two binomials have the form (A+B) and (A-B) the are called conjugate binomials.

1. you simply take the s term and square it and subtract the 2t term squared.  {{{s^2-4t^2}}} and the same for any problem with conjugate binomials
 
2.  {{{f^2-25g^2}}}

3   {{{p^2-9q^2}}}