Elements of a triangle

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Elements of a triangle are the angles that are formed when three lines intersect and the segments that mark the triangle are sides.


  • To understand the elements of a triangle

Estimated Time

40 minutes

Prerequisites/ Instructions, prior preparations, if any

Prior knowledge of point, lines, angles, parallel lines

Materials/ Resources needed

  • Digital : Computer, Geogebra application, projector.
  • Non digital : Worksheet and pencil,6-8 strings (preferably in different colours)
  • Geogebra files : Elements of a triangle.ggb

Process (How to do the activity)

  • Student groups can be formed, students in their group do the following activity individually.
  • Take the strings and place them in such a way as to make a closed figure.
  • What is the smallest number of strings with which you can form a closed figure?
  • What is this figure called?
  • Can you just draw the lines along the strings and see what you get?
  • When you drew, what did you draw?  (Was it a line or was it an angle or was it a line segment?). It is a lime segment – how many line segments are there?
  • When two line segments joined, what is it called?  (A vertex). How many vertices are there?
  • Is there any angle formed when you made this figure? How many angles were formed? How many angles lie within the closed figure?
  • Show a simple Geogebra file with triangles – Use this file to demonstrate that every triangle has the elements - vertices, sides and angles
  • How many triangles were formed?  Were there any strings left over?
  • For each of the triangles trace the shape on the book and write down the elements of the triangle in the following format
Vertices Sides Angles
  • For each of the triangles observe (inspect visually) which is the longest side and which is the shortest side
Triangle name Largest angle Largest side Smallest angle Smallest side
  • Allow the students to explore if there is any connection between the two?
  • After the students see the Geogebra file, they can attempt an alternative worksheet like below
Side 1 Angle 1

(opposite angle)

! Side 2 Angle 2

(opposite angle)

! Side 3 Angle 3

(opposite angle)

! Largest side and angle


! Smallest side and angle



Evaluation at the end of the activity

  • Have the students been able to identify the elements in a triangle?
  • Have they been able to extrapolate any connection between the angle and side in a triangle?