Rods and Triangles


Rods and Triangles

Pupils work with the properties of triangles through combining a range of rods to make different types of triangle.

Practical details

National Curriculum levels 4 to 7
About 30 minutes
Paper, compasses, angle measurer, ruler

Key Processes involved

Identify the triangles, showing the properties of the side lengths and describing the angles; justify their responses through mathematical diagrams or other means
Communicating and reflecting
Present work so that others can follow the reasoning

Teacher guidance

You may wish to introduce the task by showing the slides on a whiteboard.

  • You are asked to combine rods to make as many different triangles as you can.
  • You are given the length of the rods and two examples of triangles you can make.
  • Use everything you know about triangles and present your work so that it can be understood – and the reasons for what you are doing.
  • Don’t forget to look for a combination of rods that cannot be made into a triangle.

The task requires knowledge of properties of triangles and simple geometric construction. Justification should be given for any reference to acute, obtuse or right-angled triangles. During the work, the following probing questions may be helpful:

  • What types of triangle do you know? What are the properties of each type?
  • How can you check whether three rods can or cannot make a triangle?
  • How can you convince me that a triangle must be right-angled?

Six different types of triangle can be made using the rods:

eg. using rods of 4, 6 + 8 cm
eg. using rods of 6, 2 + 4, 8 cm
eg. using rods of 4 + 6, 2 + 8, 10 cm
Acute (-angled)
eg. using rods of 8, 4 + 6, 2 + 10 cm
Obtuse (-angled)
eg. using rods of 4, 6, 8 cm
Right (-angled)
eg. using rods of 6, 8, 10 cm