# Question #dc78e

$S {\in}^{2} \left(\frac{2 \pi}{7}\right) + {\cos}^{2} \left(\frac{2 \pi}{7}\right)$ would be equal to 1, because the identity ${\sin}^{2} \theta + {\cos}^{2} \theta = 1$ for all values of $\theta$