Objective: To verify that the sum of the angles of a triangle is 180o




Lets verify that the sum of the angles of a triangle is 180o.

Materials Required

1. Hardboard sheet
2. Glazed papers
3. Sketch pens/pencils
4. Scissors
5. Tracing paper
6. Adhesive
7. Drawing sheet
8. Geometry box.

Procedure

1. Take a hardboard sheet of a convenient size and paste a white paper on it.

2. Cut out a triangle from a drawing sheet, and paste it on the hardboard and name it as ΔABC.

3. 3. Mark its three angles.

4. Cut out the angles respectively equal to ∠A, ∠B and ∠C from a drawing sheet using tracing paper.

verify sum of the angles of a triangle

5. Draw a line on the hardboard and arrange the cut-outs of three angles at a point O. See the reference image below.

sum of the angles is 180

Demonstration

The three cut-outs of the three angles A, B and C placed adjacent to each other at a point form a line forming a straight angle = 180o. It shows that sum of the three angles of a triangle is 180o. Therefore, ∠A + ∠B + ∠C = 180o.

Observation

Measure of ∠A = ....................

Measure of ∠A = ....................

Measure of ∠A = ....................

Sum (∠A + ∠B + ∠C) = ............

Result

Thus, the sum of the three angles of a triangle is 180o

Application

This result may be used in a number of geometrical problems such as to find the sum of the angles of a quadrilateral, pentagon, etc.


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