## Trigonometry (11th Edition) Clone

$x=-\frac{1}{2}$
Use a calculator to fund the value of $arctan{(1)}$ to obtain: $\arccos{(x)}+\frac{\pi}{4}=\frac{11\pi}{12} \\\arccos{(x)}=\frac{11\pi}{12}-\frac{\pi}{4} \\\arccos{(x)}=\frac{2\pi}{3}$ RECALL: $\arccos{(x)}=\theta \longrightarrow \cos{\theta} = x$ Use the rule above to obtain: $\arccos{(x)}=\frac{2\pi}{3} \\\cos{(\frac{2\pi}{3})}=x \\-\frac{1}{2}=x$