(2a-b)²+x²-4ax+2bx
=x²-2x(2a-b)+(2a-b)²
=(x-2a+b)²
xy+1-x-y
=xy-x+1-y
=x(y-1)-(y-1)
=(y-1)(x-1)x²-xy-2y²-x-y=?=(x-2y)(x+y)-(x+y)=(x+y)(x-2y-1)