# Rods and Triangles

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

# Practical details

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

# Key Processes involved

Analysing
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:

Scalene
eg. using rods of 4, 6 + 8 cm
Isosceles
eg. using rods of 6, 2 + 4, 8 cm
Equilateral
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