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Finding the foci of a given ellipse
Click here for a printable ellipse construction worksheet
How find the
focus points (foci) of a given ellipse.
We start with an ellipse, defined by the four endpoints of its
major and minor axes.
We end up with the two focus points defined.
Instructions Click on 'Next' to go through the construction one step at a time, or click on 'Run' to let it run without stopping.
(If there is no image below, see support page.)
Step-by-step Instructions
| Step 1 |
With the compass point on the center, set the compass width to half the width (major axis) of the ellipse. |
| Step 2 |
Move the compass point to one end of the minor axis of the ellipse and draw two arcs across the major axis. |
| Step 3 |
Where these arcs cross the major axis are the foci of the ellipse. Label them F1, F2. |
| Step 7 |
Done. The two points F1, F2, define the foci of the ellipse. |
Try it yourself
Click here for a printable worksheet containing an ellipse drawing problem.
When you get to the page, use the browser print command to print as many as you wish. The printed output is not copyright.
Other constructions
Lines
Angles
Triangles
Triangle Centers
Circles, Arcs and Ellipses
Non-Euclidean constructions
(C) 2007 Copyright John Page
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