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. . . .
Measure the two angles. What do you notice?
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.
The area of a regular pentagon looks about twice as a big as the pentangle star drawn within it. Is it?
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. . . .
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.
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.
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?
Draw some stars and measure the angles at their points. Can you find and prove a result about their sum?
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.
Drawing the right diagram can help you to prove a result about the angles in a line of squares.
Can you work out how these polygon pictures were drawn, and use that to figure out their angles?
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).
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
Given an equilateral triangle inside an isosceles triangle, can you find a relationship between the angles?
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?
Creating designs with squares - using the REPEAT command in LOGO.
This requires some careful thought on angles
An equilateral triangle rotates around regular polygons and
produces an outline like a flower. What are the perimeters of the
This LOGO Challenge emphasises the idea of breaking down a problem
into smaller manageable parts. Working on squares and angles.
What can you say about the angles on opposite vertices of any
cyclic quadrilateral? Working on the building blocks will give you
insights that may help you to explain what is special about them.
Show that among the interior angles of a convex polygon there
cannot be more than three acute 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?
More Logo for beginners. Learn to calculate exterior angles and draw regular polygons using procedures and variables.
How can you make an angle of 60 degrees by folding a sheet of paper
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?
Prove that the internal angle bisectors of a triangle will never be
perpendicular to each other.
Can you explain why it is impossible to construct this triangle?
Which hexagons tessellate?
Turn through bigger angles and draw stars with Logo.
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?
Semi-regular tessellations combine two or more different regular polygons to fill the plane. Can you find all the semi-regular tessellations?
How many different triangles can you make which consist of the
centre point and two of the points on the edge? Can you work out
each of their angles?