Semi-regular tessellations combine two or more different regular polygons to fill the plane. Can you find all the semi-regular tessellations?

Can you find triangles on a 9-point circle? Can you work out their angles?

Interior angles can help us to work out which polygons will tessellate. Can we use similar ideas to predict which polygons combine to create semi-regular solids?

What is the relationship between the angle at the centre and the angles at the circumference, for angles which stand on the same arc? Can you prove it?

Show that among the interior angles of a convex polygon there cannot be more than three acute angles.

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

Can you explain why it is impossible to construct this triangle?

Investigate the different ways of cutting a perfectly circular pie into equal pieces using exactly 3 cuts. The cuts have to be along chords of the circle (which might be diameters).

Points D, E and F are on the the sides of triangle ABC. Circumcircles are drawn to the triangles ADE, BEF and CFD respectively. What do you notice about these three circumcircles?

Can you work out how these polygon pictures were drawn, and use that to figure out their angles?

Draw some stars and measure the angles at their points. Can you find and prove a result about their sum?

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.

Draw some quadrilaterals on a 9-point circle and work out the angles. Is there a theorem?

The three corners of a triangle are sitting on a circle. The angles are called Angle A, Angle B and Angle C. The dot in the middle of the circle shows the centre. The counter is measuring the size. . . .

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?

An equilateral triangle rotates around regular polygons and produces an outline like a flower. What are the perimeters of the different flowers?

Prove that the internal angle bisectors of a triangle will never be perpendicular to each other.

Given an equilateral triangle inside an isosceles triangle, can you find a relationship between the angles?

Creating designs with squares - using the REPEAT command in LOGO. This requires some careful thought on angles

This LOGO Challenge emphasises the idea of breaking down a problem into smaller manageable parts. Working on squares and angles.

Drawing the right diagram can help you to prove a result about the angles in a line of squares.

Measure the two angles. What do you notice?

More Logo for beginners. Learn to calculate exterior angles and draw regular polygons using procedures and variables.

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.

Follow instructions to fold sheets of A4 paper into pentagons and assemble them to form a dodecahedron. Calculate the error in the angle of the not perfectly regular pentagons you make.

Triangle ABC has a right angle at C. ACRS and CBPQ are squares. ST and PU are perpendicular to AB produced. Show that ST + PU = AB

The centre of the larger circle is at the midpoint of one side of an equilateral triangle and the circle touches the other two sides of the triangle. A smaller circle touches the larger circle and. . . .

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.

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

Turn through bigger angles and draw stars with Logo.

Make five different quadrilaterals on a nine-point pegboard, without using the centre peg. Work out the angles in each quadrilateral you make. Now, what other relationships you can see?