Circles and Circle Theorems - February 2004, Stage 4&5

Problems

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Weekly Problem 39 - 2011

Stage: 4 Challenge Level: Challenge Level:1

Of these five figures, which shaded area is the greatest? The large circle in each figure has the same radii.

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Circle-in

Stage: 4 Challenge Level: Challenge Level:1

A circle is inscribed in a triangle which has side lengths of 8, 15 and 17 cm. What is the radius of the circle?

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Circle Box

Stage: 4 Challenge Level: Challenge Level:2 Challenge Level:2

It is obvious that we can fit four circles of diameter 1 unit in a square of side 2 without overlapping. What is the smallest square into which we can fit 3 circles of diameter 1 unit?

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Circle Scaling

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

You are given a circle with centre O. Describe how to construct with a straight edge and a pair of compasses, two other circles centre O so that the three circles have areas in the ratio 1:2:3.

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Circles in Circles

Stage: 5 Challenge Level: Challenge Level:1

This pattern of six circles contains three unit circles. Work out the radii of the other three circles and the relationship between them.

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Lunar Angles

Stage: 5 Challenge Level: Challenge Level:2 Challenge Level:2

What is the sum of the angles of a triangle whose sides are circular arcs on a flat surface? What if the triangle is on the surface of a sphere?

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Flower

Stage: 5 Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3

Six circles around a central circle make a flower. Watch the flower as you change the radii in this circle packing. Prove that with the given ratios of the radii the petals touch and fit perfectly.