Show That $\left( - \frac { 2 \sqrt { 2 } } { 3 } , - \frac { 1 } { 3 } \right)$

Essay

Show that $\left( - \frac { 2 \sqrt { 2 } } { 3 } , - \frac { 1 } { 3 } \right)$ is on the unit circle.