Take positive root for real chance (positive terms): $ x = \frac-21 + 3\sqrt714 $. Compute numerically: $ \sqrt7 \approx 2.6458 $, $ 3\sqrt7 \approx 7.937 $, so $ x \approx \frac-21 + 7.93714 = \frac-13.06314 \approx -0.932 $. Then $ \frac1x \approx -1.073 $, so $ 1 + 2(-1.073) = -1.146 $. Not meaningful.