Answer
$\theta = 0^{\circ}, 180^{\circ}, 360^{\circ}$
Work Step by Step
$\cos^2 \theta = \sin^2 \theta + 1$
$\cos^2 \theta - \sin^2 \theta = 1$
$\cos 2\theta = 1$
$2\theta = 0^{\circ}, 360^{\circ}, 720^{\circ}$
$\theta = 0^{\circ}, 180^{\circ}, 360^{\circ}$
