## Precalculus (6th Edition) Blitzer

$\dfrac{\pi}{4}$
The reference angle of an angle $0 \leq \theta \lt 2\pi$ based on its position can be computed by using the following steps: a) Quadrant- I: $\theta$ b) Quadrant -II: $(\pi-\theta)$ c) Quadrant- III: $(\theta - \pi)$ d) Quadrant - IV: $(2\pi - \theta)$ We can see that the angle $\dfrac{11\pi}{4}$ is close to $\dfrac{12\pi}{4}=3\pi$. Thus, the reference angle of $\dfrac{11\pi}{4}$ is: $= 3\pi - \dfrac{11\pi}{4}$ $\implies =\dfrac{12\pi}{4} - \dfrac{11\pi}{4}$ $=\dfrac{\pi}{4}$