Solve the Problem $\theta$ , the Water Level L Behind the Wheel Changes According

Essay

Solve the problem.
-A water wheel rotates through the angle $\theta$ , the water level L behind the wheel changes according to the equation $\mathrm { L } = 1 - \sin \theta - 2 \cos ^ { 2 } \theta$ where L is measured in inches. Determine the values of $\theta$ for which the water level is zero. Find the exact values.
Do not use a calculator.