# 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.

### Objectives

- 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
ex-side1,angle1 |
! Smallest side and angle
ex-side3,angle3 |
---|---|---|---|---|---|---|---|

. | |||||||

. | |||||||

. |

**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?