Answer
$$r=\frac{\sqrt{177}+3}{14},\:r=\frac{-\sqrt{177}+3}{14}$$
Work Step by Step
Completing the square to solve the equation, we find:
$$ 7\left(\left(r-\frac{3}{14}\right)^2-\frac{6}{7}-\left(-\frac{3}{14}\right)^2\right) \\ 7\left(r-\frac{3}{14}\right)^2-\frac{177}{28} \\ \left(r-\frac{3}{14}\right)^2=\frac{177}{196} \\ r=\frac{\sqrt{177}+3}{14},\:r=\frac{-\sqrt{177}+3}{14}$$
