what is the exact value of tan- 13pi/6

\(\tan\left(-\dfrac{13\pi}{6}\right) = \tan\left(-\dfrac{\pi}{6}\right)=\\ \dfrac{\sin \left (-\frac{\pi}{ 6} \right) }{\cos\left(-\frac \pi 6 \right)} =\dfrac{-\frac 1 2}{\frac{\sqrt{3}}{2}} = -\dfrac{1}{\sqrt{3}}\)

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