x^2-4y^2-x+2y
=(x^2-x+1/4)-1/4-(4y^2-2y+1/4)+1/4
=(x-1/2)^2-(2y-1/2)^2
=(x+2y+1)(x-2y)
x^2-2x-b^2-2b
=(x^2-2x+1)-1-(b^2+2b+1)+1
=(x-1)^2-(b+1)^2
=(x+b)(x-b-2)