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Here the path of Q (the red vertical line) has been moved slightly to the right.
What happens to the circle that the image of Q lies on?
[What happens if the path of Q (the red vertical line) is moved further still, so that it lies entirely outside the given circle?]

On the next page we look at a way of proving that the image of our original line segment BD lies on a circle.
However, you might first want to use the JAVA worksheets to explore the configuration in a more interactive way.
JAVA worksheet A allows you to explore what happens when B (and hence the red line) is moved to other positions inside the circle.
JAVA worksheet B allows you to drag an object (point R) completely freely (for example in a circle as a prelude to the Method B1 and Method B2 pages).