Which is itself is just special case of difference of squares property: x^2 - y^2 = (x - y) * (x + y) In this case y is 1 and y^2 is 1, so this gives us afore

Which is itself is just special case of difference of squares property: x^2 - y^2 = (x - y) * (x + y) In this case y is 1 and y^2 is 1, so this gives us aforementioned: x^2 - 1 = (x - 1) * (x + 1) Here is wikipedia page with the proof: http://en.wikipedia.org/wiki/Difference_of_two_squares http://en.wikipedia.org/wiki/Difference_of_two_squares