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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?

Nicely Similar

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

In the diagram below, a right-angled triangle has a line descending from its right angle, perpendicular to the hypotenuse.

diagram with similar right-angled triangles


If the hypotenuse length is 100cm, and if the line splits the base into 36cm and 64cm parts, what are the side lengths of the original right-angled triangle?

For another way to see this arrangement of right-angled triangles you may like to look at the problem called a Matter of Scale .