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Golden Thoughts

Rectangle PQRS has X and Y on the edges. Triangles PQY, YRX and XSP have equal areas. Prove X and Y divide the sides of PQRS in the golden ratio.

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The diagram shows a regular pentagon with sides of unit length. Find all the angles in the diagram. Prove that the quadrilateral shown in red is a rhombus.

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ABCDE is a regular pentagon of side length one unit. BC produced meets ED produced at F. Show that triangle CDF is congruent to triangle EDB. Find the length of BE.

Darts and Kites

Age 14 to 16 Challenge Level:

A rhombus, PQRS.

The diagram shows a rhombus $PQRS$ with an internal point $O$ such that $OQ = OR = OS = 1$ unit. Penrose used this rhombus, split into two quadrilaterals, a dart and a kite, to make his famous tiling which fills the plane but, unlike a tessellation, does not repeat itself by translation or rotation.

Find all the angles in the diagram, show that $POR$ is a straight line and show that triangles $PRS$ and $QRO$ are similar. Hence prove that the length of the side of the rhombus is equal to the Golden Ratio $(1+ \sqrt{5})/2$.