## Functions Modeling Change: A Preparation for Calculus, 5th Edition

$$θ=\frac{\pi }{4}$$
To evaluate trigonometric functions without a calculator, it is necessary to use the unit circle. Doing this, we find that theta is: $$\cos \left(θ\right)=\frac{\sqrt{2}}{2} \\ θ=\frac{\pi }{4}$$