To find a radius you must first draw a circle with a compass, a compass is a mathematical tool used to draw a precise circle.
You then must find the centre of the circle, you can do this by seeing where the sharp part of your compass is after you finish drawing the circle.
Draw a straight line with a ruler from the centre of the circle to the edge.
You then must measure the length from the centre of the circle to the edge with a ruler.
Then you have the radius of the circle!
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