\( \definecolor{colordef}{RGB}{249,49,84} \definecolor{colorprop}{RGB}{18,102,241} \)
Express \(\cos\left(\frac{13\pi}{6}\right)\) in terms of cosine or sine of \(\frac{\pi}{6}\) (use a unit circle):
\(\cos\left(\frac{13\pi}{6}\right) = \)