It has the sign of for all values of . This means that, if , the concavity is upward directed everywhere; if , the concavity is downward directed; for , the curvature is zero everywhere, confirming that the parabola degenerates into a line in this case.
it hAs ThE siGn Of FOr aLl valueS oF . THiS meAnS thAt, if , thE cONCaViTY iS upwaRd DIRected eVErywherE; IF , the concaVity is downwArD diREcteD; FOr , thE cuRVaTuRe Is zero EverYwHeRE, Confirming thAt thE pAraBOla degEnERAtEs iNto a liNe iN THiS case.