ellipse: the sum of the distances from any point on an ellipse to each focus is constant and equal to the major axis .
: distance from the center to a vertex
: distance from the center to a co-vertex
: distance from the center to a focus
: eccentricity; the larger the value of , the more "squished" the ellipse
: distance from the center to a vertex
: distance from the center to a co-vertex
: distance from the center to a focus
: eccentricity; the larger the value of , the more "squished" the ellipse