# Formation of a triangle

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Introducing formation of a shape with least number of lines and the space enclosed by these lines form a geometric shape.The key geometric concepts that are related with this are explained.

### Objectives

- Understand formation of triangles
- Recognize elements of triangle
- Introduce concepts of exterior angle.

### Estimated Time

30 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
- Geogebra files :
**“Introduction to a triangle.ggb”**

Download this geogebra file from this link.

### Process (How to do the activity)

- Use the geogebra file to illustrate. The questions below will are used to interact with the geogebra sketch.
- How many lines are there? Are the lines meeting?
- Are the two lines parallel? How can you say they are parallel or not?
- How many angles are formed at the point of intersection?
- What is the measure of the total angle at the point of intersection of two lines?
- Of the four angles formed which of the angles are equal? What are they called?
- Do the three intersecting lines enclose a space? How does it look? It is called a triangle.
- What are the points of intersection of these three lines called?
- The line segments forming the triangle are called sides.
- How many angles are formed when three lines intersect with each other?
- How many angles are enclosed by the triangle?

**Evaluation at the end of the activity**

- Can there be a closed figure with less than three sides?
- Can the vertices of the triangle be anywhere on a plane?
- What will happen if the three vertices are collinear?