## Precalculus (6th Edition) Blitzer

$\frac{x^2}{100}+\frac{y^2}{51}=1$
Step 1. With the given conditions, we have $c=\frac{7+7}{2}=7, a=\frac{10+10}{2}=10, b=\sqrt {10^2-7^2}=\sqrt {51}$ Step 2. We can write the equation as $\frac{x^2}{100}+\frac{y^2}{51}=1$