## Trigonometry (10th Edition)

1. With $-90^{\circ}\lt \theta\lt 90^{\circ}$, then $90^{\circ}\lt \theta+180^{\circ}\lt 270^{\circ}$ 2. This means that $\theta +180^{\circ}$ is in QII or QIII, where $x\lt0$ 3. Therefore $sec( \theta+180)^{\circ}\gt 0$