解(2x-y-3）^2=[2x-(y+3)]^²=(2x)^2-2×2x（y+3）+（y+3）^2=4x^2-4xy-12x+y^2+6y+9=4x^2+y^2-4xy-12x+6y+9与解(2x-y-3）^2=[2x-(y+3)]^2=(2x)^2-2×2x（y+3）+（y+3）^2=4x^2-4xy-12x+y^2+6y+9=4x^2+y^2-4xy-1...