Ellipses

If an ellipse has its major axis along the y-axis and is centered at (0, 0), the standard form becomes:

The endpoints of the major axis become (0, a) and (0, -a). The endpoints of the minor axis are (b, 0) and ( ?b, 0). The foci are at (0, c) and (0, -c), with c² = a² - b² .

When an ellipse is written in standard form, the major axis direction is determined by noting which variable has the larger denominator. The major axis either lies along that variable's axis or is parallel to that variable's axis.