(2x+y+1)(2x-y-1)=[2x+(y+1)][2x-(y+1)]=(2x)^2-(y+1)^2=4x^2-y^2-2y-1
(3x-y-1)^2=[3x-(y+1)]^2=(3x)^2-2*3x*(y+1)+(y+1)^2=9x^2-6x-6xy+y^2+2y+1