Interior and exterior angles in triangle
Objectives
- Identify all angles when a triangle is formed
- Understand the relation between various angles that are formed in a triangle.
Estimated Time
Prerequisites/Instructions, prior preparations, if any
Prior knowledge of point, lines, angles
Materials/ Resources needed
- Digital : Computer, geogebra application, projector.
- Non digital : Worksheet and pencil.
- Geogebra files : “Angles of triangle.ggb”
Process (How to do the activity)
- Ask students how many lines are there? They should be able to identify the points of intersection of the lines. How many points of intersection are formed?
- How many angles are formed at an intersecting point? How many angles in total at the three points of intersection?What is the total angle measure at each intersecting point?
- How many angles are inside the triangle and how many are outside the triangle
- Can you find an exterior angle that is equal to the interior angle of a triangle at each vertex?Why are they equal?
- Identify the exterior angles that are equal? Justify why they are equal.
- Establish that there are 2 angles which are exterior of the triangle that are equal and are formed when the sides of the triangle is extended at the vertex.
- Students to analyze the interior and exterior angle at each point to find a relation between the interior angle and one of the exterior angles at the vertex. Students should be able to recognize the linear pair formed by interior angle and exterior angle.
- Vary the position of the lines to check if interior and exterior angles form a linear pair.
- Note the measure of angles
| Angles of the triangle | Exterior angle | Interior angle + Exterior angle | ||||||
|---|---|---|---|---|---|---|---|---|
| Angle 1 | Angle 2 | Angle 3 | Angle 1 | Angle 2 | Angle 3 | In Angle 1
+ Ex Angle1 |
In Angle 2
+ Ex Angle2 |
In Angle 3
+ Ex Angle3 |
Evaluation at the end of the activity
- Are students able to recognize interior and exterior angles in a triangle
- Have the students able to find a relation between the interior angle and exterior angle that are formed at each vertex?