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Ellipse (string and optical properties)

This video uses the string property of an ellipse to help you construct an ellipse. To keep the definition simple, if you pick any point on the the ellipse, the sum of the distance of that point to the foci will be the same as 2a, or the length of the ellipse along the major axis. http://ggbm.at/Km3uQ6cC Materials needed: paper, marker, corkboard, string, 2 pins Instructions: 1. Draw two points, label them F1 and F2. (You definitely do not have to put them on a specific axis, I used this activity to help students derive other equations, so we needed to have it set up as you see in the video.) 2. Place pins in at both points. 3. Take your string, tie it into a loop, and, keeping the string taut, complete your ellipse as shown. 4. Try measuring your ellipse along the axis and pick a point X on the ellipse to see if it really matches the definition. OPTICAL PROPERTY: https://www.geogebra.org/o/TwYEtRbG A ray of light (or sound) emanating from one foci will bounce off the side and hit the other foci. (Again, I don't have any audio for these videos, since I use them to enrich my instruction. You can say what you want with these videos!) *If you have any requests for videos, let me know in the comment section.*