Answer:
[tex]\large\boxed{\Theta=\dfrac{2\pi}{3}\ \vee\ \Theta=\dfrac{4\pi}{3}}[/tex]
Step-by-step explanation:
[tex]-2\cos\Theta=-3-8\cos\Theta\qquad\text{add}\ 8\cos\Theta\ \text{to both sides}\\\\6\cos\Theta=-3\qquad\text{divide both sides by 6}\\\\\cos\Theta=-\dfrac{3}{6}\\\\\cos\Theta=-\dfrac{1}{2}\\\\\text{look at the picture}\\\\\Theta=\dfrac{2\pi}{3}\ \vee\ \Theta=\dfrac{4\pi}{3}[/tex]
