$\lambda =-\sqrt{7}\left(\sqrt{3}\sin(\frac{\arccos(\frac{5\sqrt{7}}{49})}{3})+\cos(\frac{\arccos(\frac{5\sqrt{7}}{49})}{3})\right)\approx -4.322810445$
$\lambda =2\sqrt{7}\cos(\frac{\arccos(\frac{5\sqrt{7}}{49})}{3})\approx 4.804316948$
$\lambda =\sqrt{7}\left(\sqrt{3}\sin(\frac{\arccos(\frac{5\sqrt{7}}{49})}{3})-\cos(\frac{\arccos(\frac{5\sqrt{7}}{49})}{3})\right)\approx -0.481506503$