X^2-2X-4Y^2-4Y=（X^2-2X+1）-（4Y^2+4Y+1）=（x-1）^2-(2y+1)^2=(x-1+2y+1)(x-1-2y-1)=(x+2y)(x-2y-2)
(x-2y-2)(x+2y)
x^2-2x-4y^2-4y=(x^2-4y^2)-(2x+4y)=(x+2y)(x-2y)-2(x+2y)=(x+2y)(x-2y-2)
