CPM Homework Help : A2C Problem 12-151

Where is the $\operatorname{tan} θ$ undefined? Use the unit circle to support your answer.

Hint:

$\text{Remember} \operatorname{tan}\theta=\frac{\operatorname{sin}\theta}{\operatorname{cos}\theta}.$

Where is $\operatorname{cos}θ = 0$ ?