if cos theta = 2/3 find tan theta
could be 1st or 4th quad
adj = 2
hyp = 3
opp = $${\sqrt{{\mathtt{9}}{\mathtt{\,-\,}}{\mathtt{4}}}} = {\sqrt{{\mathtt{5}}}}$$
$$tan\theta=\frac{opp}{adj}=\pm \frac{\sqrt{5}}{2}$$
