Question

Find the center, vertices, and foci of the ellipse with equation 2x2 + 8y2 = 16.

Answer 1

$\bf \textit{ellipse, horizontal major axis} \\\\ \cfrac{(x- h)^2}{ a^2}+\cfrac{(y- k)^2}{ b^2}=1 \qquad \begin{cases} center\ ( h, k)\\ vertices\ ( h\pm a, k)\\ c=\textit{distance from}\\ \qquad \textit{center to foci}\\ \qquad \sqrt{ a ^2- b ^2} \end{cases} \\\\[-0.35em] \rule{34em}{0.25pt}$

$\bf 2x^2+8y^2=16\implies \cfrac{2x^2+8y^2}{16}=1\implies \cfrac{2x^2}{16}+\cfrac{8y^2}{16}=1\implies \cfrac{x^2}{8}+\cfrac{y^2}{2}=1 \\\\\\ \cfrac{(x-0)^2}{(\sqrt{8})^2}+\cfrac{(y-0)^2}{(\sqrt{2})^2}=1\qquad \begin{cases} a=\sqrt{8}\\ b=\sqrt{2}\\ c=\sqrt{a^2-b^2}\\ \qquad \sqrt{6} \end{cases}~\hfill \begin{array}{llll} \stackrel{\textit{vertices}}{(\pm \sqrt{8},0)}\qquad \stackrel{\textit{foci}}{(\pm \sqrt{6},0)}\\\\ ~\hfill \stackrel{\textit{center}}{(0,0)}~\hfill \end{array}$