There are some special situations that have special methods of factoring. Once such situation is the factoring the difference of two perfect squares. You need to know this formula!
Factoring the Difference of Two Squares 


We already know that by multiplying: (a + b)(a  b) = a^{2}  b^{2}.
If we use the commutative property on this equation we get:
a^{2}  b^{2 }= (a + b)(a  b) 
which shows a formula for factoring a^{2}  b^{2}, the difference (subtraction) of two perfect squares.
Notice that the factors are identical except that one is addition and the other is subtraction.