Lab Manual: Verify Exterior Angle Property of a Triangle | Lab Manuals for Class 9 PDF Download

Objective

Materials Required
Cardboard sheet, Adhesive, Glazed papers, White chart paper, Geometry box, Tracing paper, Cutter

Prerequisite Knowledge

• Straight angle
• Exterior angle property of a triangle.

Theory

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

Procedure

• Take a cardboard sheet of suitable size and by using adhesive, paste a white chart paper on it.
• Cut out a ΔABC from a glazed paper and paste it on the cardboard, (see Fig. 13.1)

• Now, produce the side BC of ΔABC to the point D. (see Fig. 13.2)
  
• Cut out the pair of angles, ∠A and ∠B from the glazed paper by using a tracing paper, (see Fig. 13.3).
• Now, arrange the cut out angles as shown in Fig. 13.4.
  

Demonstration
From Fig. 13.4,

• ∠ACD is an exterior angle.
• ∠A and ∠B are its two interior opposite angles.
• 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.

Application
Many geometrical problems may be easily done, using this property of a triangle.