Answer
$-\dfrac{11\pi}{6}$
Work Step by Step
$\because \theta \text{ and } \theta - 2n \pi \text{ represent the same angle}$
$\text{Where } n \text{ is an integer}$
$\text{For } n=1, \text{ an equivalent negative angle to } \dfrac{\pi}{6} \text{ is:}$
$$\dfrac{\pi}{6}-2\pi = -\dfrac{11\pi}{6}$$
