Chapter 11 - Sequences; Induction; the Binomial Theorem - Section 11.2 Arithmetic Sequences - 11.2 Assess Your Understanding - Page 836: 72

$\frac{x^2}{4}+\frac{y^2}{25}=1$ See graph.

1. Given $25x^2+4y^2=100$, we have $\frac{x^2}{4}+\frac{y^2}{25}=1$ which represents an ellipse with center $(0,0)$, vertical major axis, $a=5, b=2, c=\sqrt {25-4}=\sqrt {21}$ (focus). 2. See graph.