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Symmetric Trace

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The Line and Its Strange Pair

In the diagram the point P' can move to different places along the dotted line. Each position P' takes will fix a corresponding position for P. If P' moves along a straight line what does P do ?

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Like a Circle in a Spiral

A cheap and simple toy with lots of mathematics. Can you interpret the images that are produced? Can you predict the pattern that will be produced using different wheels?

Mapping the Wandering Circle

Stage: 4 Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3



This problem builds on from The Line and Its Strange Pair - you may wish to look at that first.

Two points, one inside a circle and the other outside, are related in the following way :

A line starting at the centre of the circle and passing through the first point ( P ) goes on to pass through the second point ( P' )

Positions along the line are such that the ratio of OP to the radius of the circle matches the ratio of the radius of the circle to OP'

For example if OP happened to be 2/3 of the radius then OP' would be 3/2 of the radius.

In the diagram above, the point P can move to different places around the dotted circle.

Each position P takes will fix a corresponding position for P' .

As P moves around that circle what will P' do ?

Why?

You might find the interactivity below helpful. Holding down the mouse button leaves a trace of the points.

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