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# Parabolas

## Collection of points equidistant from a fixed focus and directrix.

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Satellite TV Dishes

### Parabolas

Credit: Jan Tik
Source: http://commons.wikimedia.org/wiki/File:Satellite_dish_(Television).jpg

[Figure1]

Do you have satellite television or know someone who has installed it? If you’ve ever seen the home of someone with a satellite television subscription, you’ve probably noticed a round, dish-shaped antennae on the roof. This satellite dish is responsible for receiving signals from outer space and delivering those signals to your television for your viewing entertainment. The dish is essentially a 3-D parabola or a paraboloid. Recall that a parabola is a curve of points equidistant (or of equal distances) of a point (the focus) and a line (the directrix). Signals bounce off of the dish, and collect together at the receiver which is placed at the focus of the dish.

### Creative Applications

1. How would moving a receiver 2 inches closer or away from the dish affect signal reception?

2. What would the be the pros of using a larger dish? The cons?

3. Why would someone choose satellite over cable television for premium television? Why would one not choose satellite?

4. Where else can parabolas be found?

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