Multiplying Polynomials 5: Difference of 2 Squares
http://www.youtube.com/watch?v=AecdR8wpIWM
Factoring 15a - Difference of 2 Squares
Covers the formula for the factoring the difference of two squares, including examples.
http://www.youtube.com/watch?v=Fwqh9vq0sq8
Factoring 15b - Difference of 2 Squares part 2
Covers more involved factoring of difference of 2 squares.
http://www.youtube.com/watch?v=PY39ZW3_B14
Factoring 16 Sum of 2 squares is prime
Emphasizes that the sum of two perfect squares usually is non-factorable over the integers and is prime.