The point (h,k) is the center. a is the major radius and b is the minor radius. [br][br][b]If the ellipse is horizontal[/b], use points [b]E[/b] and [b]F[/b] for the foci and lines [b][i]f[/i][/b] and [b][i]g[/i][/b] to help with the construction. Activate [b][i]i[/i][/b] and [b][i]j [/b][/i] to see the segments from the foci to the point on the ellipse. Activate point [b]D[/b], the point on the ellipse. Now drag point B around the circle and watch the construction.[br][br][b]If the ellipse is vertical[/b], use points [b]H[/b] and [b]I [/b] for the foci and lines [b][i]m[/b][/i] and [b][i]n[/b][/i] to help with the construction. Activate [b][i]p[/i][/b] and [b][i]q[/b][/i] to see the segments from the foci to the point on the ellipse. Activate point [b][i]G[/i][/b]. Now drag point [b][i]B[/i][/b] around the cirlce to watch the construction.

You may use this tool to help you visualize the graphs of the ellipses.