Angle sum property of triangles
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Source: IT for Change
Objectives
- To establish the angle sum property of a triangle
- To help visualization of the geometric proof
Estimated Time
30 minutes
Prerequisites/Instructions, prior preparations, if any
Prior understanding of point, lines and angles, adjacent angles, vertically opposite angles, linear pair, parallel lines, alternate angles, corresponding angles.
Materials/ Resources needed
Click here to open the file
Process (How to do the activity)
Download this geogebra file from this link.
- Students should be able to recognize the corresponding angles formed when the parallel line is drawn.
- Students should be able to recognize the alternate angles formed. Is the alternate angle same as one of the angles of the triangle.
- Ask students what happens when the three angles of the triangle are placed adjacent to each other.
- What can you say about the line drawn?
- Is it parallel to one of the sides?
- What can you say about the pairs of angles β look at the matching colours.
- Once the parallel line reaches the vertex, how many angles are formed?
- Students should be able to identify the two angles moving are corresponding angles as the line moving is parallel to one of the sides.
- Students can see that when the three angles of the triangle are placed adjacent to each other they form a straight line.
Evaluation at the end of the activity
- In a triangle, if the sum of two angles is 60Β°, then what will be the measure of third angle?
- If a triangle has all three angles are equal in measure, then what will the measure of each angle?