(midpoint is not a property of an ellipse)

(drawn with eccentricity 0.707 and semimajor axis length 1)

(x - x_0)^2/a^2 + (y - y_0)^2/b^2 = 1 (assuming center (x_0, y_0), semimajor axis length a, and semiminor axis length b)

foci | (sqrt(a^2 - b^2) + x_0, y_0) | (x_0 - sqrt(a^2 - b^2), y_0) vertices | (a + x_0, y_0) | (x_0 - a, y_0) covertices | (x_0, b + y_0) | (x_0, y_0 - b) area enclosed | π a b circumference | 4 a E(1 - b^2/a^2) focal parameter | b^2/sqrt(a^2 - b^2) eccentricity | sqrt(1 - b^2/a^2) (assuming center (x_0, y_0), semimajor axis length a, and semiminor axis length b)