Three triangles ABC, CBD and ABD (where D is a point on AC) are all isosceles. Find all the angles. Prove that the ratio of AB to BC is equal to the golden ratio.
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.
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?
Explore the geometry of these dart and kite shapes!
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
Why does this fold create an angle of sixty degrees?
Drawing the right diagram can help you to prove a result about the angles in a line of squares.
Prove that the internal angle bisectors of a triangle will never be perpendicular to each other.
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?
Semi-regular tessellations combine two or more different regular polygons to fill the plane. Can you find all the semi-regular tessellations?
Can you work out where the blue-and-red brick roads end?
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. . . .
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.
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?
Given an equilateral triangle inside an isosceles triangle, can you find a relationship between the angles?
Draw some quadrilaterals on a 9-point circle and work out the angles. Is there a theorem?
An equilateral triangle rotates around regular polygons and produces an outline like a flower. What are the perimeters of the different flowers?
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.
Turn through bigger angles and draw stars with Logo.
This LOGO Challenge emphasises the idea of breaking down a problem into smaller manageable parts. Working on squares and angles.
Creating designs with squares - using the REPEAT command in LOGO. This requires some careful thought on angles
More Logo for beginners. Learn to calculate exterior angles and draw regular polygons using procedures and variables.