$$\triangle RSP \sim \triangle ROQ \quad\to\quad$$

$$\frac{1-\sin\theta}{\cos\theta} \;=\; \frac{1}{\sec\theta + \tan\theta}$$

Trigono**graphy** Trig, if you will, the picture ...

$$\triangle RSP \sim \triangle ROQ \quad\to\quad$$

$$\frac{1-\sin\theta}{\cos\theta} \;=\; \frac{1}{\sec\theta + \tan\theta}$$