You may also like


A floor is covered by a tessellation of equilateral triangles, each having three equal arcs inside it. What proportion of the area of the tessellation is shaded?

Getting an Angle

How can you make an angle of 60 degrees by folding a sheet of paper twice?

Arclets Explained

This article gives an wonderful insight into students working on the Arclets problem that first appeared in the Sept 2002 edition of the NRICH website.

Angles Inside

Age 11 to 14 Challenge Level:
Draw a rectangle and choose a point inside. Join your point to two adjacent corners, and measure the angles as shown in the GeoGebra applet below.

Try a few examples. What do you notice?

Alison made a conjecture: "The green angle and blue angle add together to give the red angle."
Do your examples support Alison's conjecture?
Can you prove Alison's conjecture?
Can you prove it in more than one way?

What happens if you start with a parallelogram?
Or a trapezium?

What if the point goes outside the rectangle?