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Some(?) of the Parts

A circle touches the lines OA, OB and AB where OA and OB are perpendicular. Show that the diameter of the circle is equal to the perimeter of the triangle

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Rotating Triangle

What happens to the perimeter of triangle ABC as the two smaller circles change size and roll around inside the bigger circle?

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Two semicircle sit on the diameter of a semicircle centre O of twice their radius. Lines through O divide the perimeter into two parts. What can you say about the lengths of these two parts?


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

In the diagram below, the blue square is inscribed in the semicircle, and the yellow square is inscribed in the circle.

Two squares inscribed in circle and semi-circle

The blue square has an area of $40$cm$^2$.

Can you find the area of the yellow square?