Solution 10453: Designing an Ellipse Using the Geometry Section of the TI-92
How do I design an ellipse using the Geometry section of the TI-92?
Please refer to the following steps to design an ellipse on the TI-92:
• Open the Geometry Section of the TI-92 by pressing [APPS] 
• Select '3: New...'
• Select a name for this variable and press [ENTER]
• Construct a circle. (Press [F3] and select '1: Circle' )
• Construct a point (A) on the circle. Construct a point (B) inside the circle
• Connect those points with a segment.
• Construct the perpendicular bisector (press [F4] ) of the segment between points (A) and (B).
• Construct the locus of the bisector as point (A) moves on the circle -- the envelope of lines is the ellipse. This means that the line constructed is tangent to the ellipse. The point of tangency is *not* the midpoint of the segment. The locus option is under [F4]. To construct this locus, choose the locus command from the menu, select the bisector and press [ENTER], then select point (A) by pressing [ENTER].
• Construct a segment from the center to the point (A). Construct a point (C) at the intersection of the bisector line and this radius. Construct the locus of point (C) as point (A) moves on the circle. That will form an ellipse.
The TI-92 is discontinued, however, if your have other questions often times you may use the TI-89 family, TI-92 family and Voyage 200 guidebooks for additional information.