Trigonometry / Finding the exact value Given that $\cos \theta = \dfrac{-4}{5}$ and  $\sin \theta$ is positive, obtain the exact values of
$\cos (6\pi+\theta)$
i don't understand this question.

Notice that $\cos(\theta)$ is periodic with period $2\pi$, meaning that $$\cos(\theta) \equiv \cos(\theta+2\pi)\equiv\cos(\theta+4\pi) \equiv \cos(\theta+6\pi)\equiv \cos(\theta+2n\pi)$$ for $n \in \mathbb{Z}.$
Using this fact, we see that, in this case, $$\boxed{\cos(\theta+6\pi)=\cos(\theta)=-\frac{4}{5}\ \ }.$$
