Intercept Theorem

Below shows △ABC.

You can:

• shift the points A, B and C to change the position and size of △ABC.
• shift the point D to change the position of the parallel line DE.

Instructions:

1. Adjust the position and size of △ABC.
2. Check the boxes.
3. Adjust the position of the parallel line DE.
4. Observe the ratio of the lengths of AD and CD.
5. Observe the ratio of the lengths of BE and CE.
6. Repeat steps 1 ~ 5 for other positions and sizes of △ABC and other positions of the point D.

Note: To see the animation, check all boxes, then click on the "play" button (at bottom left).



Download the GeoGebra file: http://www.geogebratube.org/material/download/format/file/id/45092

Download the Worksheet: http://db.tt/7VwQWojG