Exterior angle property of a Triangle
From Karnataka Open Educational Resources
Objectives
To show that exterior angle of a triangle is equal to the sum of its interior opposite angles.
Estimated Time
30 minutes
Prerequisites/Instructions, prior preparations, if any
Knowledge about point, lines and angles, adjacent angles, alternate angles, corresponding angles, linear pair
Materials/ Resources needed
Digital : Click here to open the file
Non-digital : Worksheet, pencil, ruler, compass, protractor
Process (How to do the activity)
Download this geogebra file from this link.
Procedure:
- Draw triangle ABC
- Identify the angles of the triangle.
- What is the sum of the angles of a triangle?
- Extend one side, students should recognize the exterior angle formed.
- Measure the exterior angle of a triangle
- Identify interior opposite angles for the exterior angle of a triangle. Mark the angle in purple and green colour.
- Move the sliders and observe the changes.
- How are the two angles together related to the exterior angle?
- Do you notice any relation between the exterior angle and the interior angles
Evaluation at the end of the activity
- What would be the measure of exterior angle for each vertex of an equilateral triangle?
- Does an exterior angle of a triangle is smaller than either of its interior opposite angles?
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