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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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Ladder and Cube

A 1 metre cube has one face on the ground and one face against a wall. A 4 metre ladder leans against the wall and just touches the cube. How high is the top of the ladder above the ground?

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At a Glance

The area of a regular pentagon looks about twice as a big as the pentangle star drawn within it. Is it?

The Medieval Octagon

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


Medieval stonemasons used this method to construct exact octagons in a given square window.

Open your compasses to a radius of half the diagonal of the square and construct an arc with centre one vertex of the square - mark the 2 points where the arc crosses the sides.

Do that for all 4 vertices of the square giving 8 points which are the vertices of an octagon. Is the octagon an exact regular octagon ? Proof please.

If you have a Java enabled browser you can experiment with the interactive version