Answer
$\dfrac{\pi}{6}$
Work Step by Step
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: $(2\pi - \theta)$
Thus, the reference angle is:
$ = \dfrac{25\pi}{6} -4\pi $
$\implies =\dfrac{25 \pi}{6} - \dfrac{24 \pi}{6}$
$ =\dfrac{\pi}{6}$
