## Precalculus (6th Edition) Blitzer

$d=10sec(x)$
Step 1. Based on the given conditions, we have $cos(x)=\frac{10}{d}$ which gives $d=10sec(x)$ Step 3. We can graph the function for $-\frac{\pi}{2}\lt x\lt \frac{\pi}{2}$ as shown in the figure.