Write the value of △ = ∣∣∣∣x+yy+zz+xzxy∣∣∣∣

On expansion, we get, ∣∣∣∣x+yy+zz+xzxy∣∣∣∣=(x+y)(x+3y)-(y+z)(z+3y)+(z+x)(z+3x) = (x^2+3xy+xy+3y^2)-(y^2+3y^2+yz+3yz)+(z^2+3xz+xz+3x^2) = (x^2+4xy+3y^2)-(4y^2+4yz)+(z^2+4xz+3x^2) = x^2+4xy+3y^2-4y^2-4yz+z^2+4xz+3x^2 = 4x^2+4xy+4xz-y^2-4yz+z^2