=(x-2y)(x+y）-x+5y-2
=(x-2y)(x+y）-2x+x+y+4y-2
=(x-2y)(x+y)+(x+y)-2x+4y-2
=(x+y)(x-2y+1)-2(x-2y+1)
=(x-2y+1)(x+y-2)