## Trigonometry (11th Edition) Clone

$y=\frac{2\pi}{3}$
RECALL: $y=\cos^{-1}{x} \longrightarrow \cos{y}=x$ Note that $\cos{(\frac{2\pi}{3})}=-\frac{1}{2}$. Therefore, $y=\cos^{-1}{(-\frac{1}{2})}\longrightarrow y=\frac{2\pi}{3}$