x^2-3y^2-8z^2+2xy+2xz+14yz
=(x^2+y^2+z^2+2xy+2xz+2yz)-4y^2-9z^2+12yz
=(x+y+z)^2-(2y-3z)^2
=(x+y+z+2y-3z)(x+y+z-2y+3z)
=(x+3y-2z)(x-y+4z)