## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$$\tan \theta=\frac{b}{a}.$$
We know that $\tan \theta=\frac{y}{x}$. This can also be thought of as $\frac{opposite}{adjacent}$ (recall SOH-CAH-TOA). Thus, we have: $$\tan \theta=\frac{b}{a}.$$