2010^2-2011*2009+2009*2+2009^2
=2010^2-(2010+1)*(2010-1)+2009*2+2009^2
=2010^2-(2010^2-1)+2009*2+2009^2
=2010^2-2010^2+1+2009*2+2009^2
=1+2009*2+2009^2
=(2009+1)^2
=2010^2
(2x-5)(2x+5)-(2x+1)(2x-3)
=4x^2-25-(4x^2-4x-3)
=4x^2-25-4x^2+4x+3
=4x^2-4x^2+4x+3-25
=4x-22