Answer
$\dfrac{2\sqrt3}{3}$
Work Step by Step
We know that $\sin$, $\csc$, $\tan$ are odd functions, which means $f(-\theta)=-f(\theta).$
We also know that $\cos$, $\sec$, are even functions, which means $f(-\theta)=f(\theta).$
Therefore,
$\sec{\left(-\frac{\pi}{6}\right)}\\
=\sec{\left(\frac{\pi}{6}\right)}\\
=\dfrac{1}{\cos(\frac{\pi}{6})}\\
=\dfrac{1}{\frac{\sqrt3}{2}}\\
=\frac{2}{\sqrt3}\\
=\frac{2}{\sqrt3} \cdot \frac{\sqrt3}{\sqrt3}\\
=\frac{2\sqrt3}{3}$
