4x^2-4xy-a^2+y^2=(2x-y)^2-a^2=(2x-y-a)(2x-y+a)x^2-2y-4y^2+x=(x+1/2)^2-(2y+1)^2=(x-2y-1/2)(x+2y+3/2)5x^2-10xy+5y^2-2x+2y=5(x-y)^2-2(x-y)=(x-y)(5x-5y-2)4a^2+9b^2-c^2-12ab+2c-1=(2a-3b)^2-(c-1)^2=(2a-3b-c...