Activity & Practical on Verify Exterior Angle Property of a Triangle | Class 9th Mathematics-EduGrown

OBJECTIVE

To verify exterior angle property of a triangle.

Materials Required

1. Cardboard sheet
2. Adhesive
3. Glazed papers
4. White chart paper
5. Geometry box
6. Tracing paper
7. Cutter

Prerequisite Knowledge

1. Straight angle
2. Exterior angle property of a triangle.

Theory

1. For straight line refer to Activity 11.
2. For exterior angle property of a triangle refer to Activity 12.

Procedure

1. Take a cardboard sheet of suitable size and by using adhesive, paste a white chart paper on it.
2. Cut out a ΔABC from a glazed paper and paste it on the cardboard, (see Fig. 13.1)
   
3. Now, produce the side BC of ΔABC to the point D. (see Fig. 13.2)
   
4. Cut out the pair of angles, ∠A and ∠B from the glazed paper by using a tracing paper, (see Fig. 13.3).
   
5. Now, arrange the cut out angles as shown in Fig. 13.4.
   

Demonstration
From Fig. 13.4,

1. ∠ACD is an exterior angle.
2. ∠A and ∠B are its two interior opposite angles.
3. The two cut out angles, ∠A and ∠B together completely cover ∠ACD. So, ∠ACD = ∠A + ∠B.

Observation
Measure of ∠A = ……… , and ∠B = ……… ,
Sum of (∠A + ∠B) = ……… , and measure of ∠ACD = ……… ,
Therefore, ∠ACD = ∠A + ∠B.

Result
We have verified the exterior angle property of a triangle.