x2 - 2xy + y2 - x2
= (x - y)2 - x2
= (x - y -x) (x - y + x)
= -y(2x -y)
x2 - 2xy - 4x2 + y2
= (x2 - 2xy + y2) - 4x2
= (x - y)2 - 4x2
= (x - y - 2x)(x - y +2x)
(2x + 1 )2 - ( x - 1)2
= (2x + 1 - x + 1)(2x + 1 + x - 1)
= 3x( x + 2)
4a2 - 4a + 1
= (2a - 1)2
-9x2 + 6xy - y2
= - (9x2 - 6xy + y2)
= - (3x - y)2
-6x + 9 + x2
= x2 - 6x + 9
= (x - 3)2
4x2 - 4x + 1 - y2
= (2x - 1)2 - y2
= (2x - 1 - y2)(2x - 1 + y2)