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Circles

Imagine a circle *O* and a grid consisting of horizontal lines and vertical lines. The inverse of each line in *O* is a circle, so, if you start with 18 lines, then you'd also have 18 circles. Now, imagine hiding the 18 lines, but keeping the circles, and then rotating the center of *O* around the origin of the grid. To start or stop the motion, click the Animate Point button.
Can you figure out the role played by each of the red points?

For more, see **GEOMETRY IN ACTION**, Chapter 3, Project 5.