NCERT Class 9 Maths Lab Manual – Verify Exterior Angle Property of a Triangle
To verify exterior angle property of a triangle.
- Cardboard sheet
- Glazed papers
- White chart paper
- Geometry box
- Tracing paper
- Straight angle
- Exterior angle property of a triangle.
- For straight line refer to Activity 11.
- For exterior angle property of a triangle refer to Activity 12.
- 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.
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.
Measure of ∠A = ……… , and ∠B = ……… ,
Sum of (∠A + ∠B) = ……… , and measure of ∠ACD = ……… ,
Therefore, ∠ACD = ∠A + ∠B.
We have verified the exterior angle property of a triangle.
Many geometrical problems may be easily done, using this property of a triangle.
What do you mean by the linear pair axiom?
If a ray stands on a line, then the sum of the two adjacent angles so formed is 180° and vice-versa. This property is known as linear pair axiom.
What would be the measure of exterior angle for each vertex of equilateral triangle?
120° (=60°+ 60°).
Does an exterior angle of a triangle is smaller than either of its interior opposite angles?
No, an exterior angle of a triangle is greater than either of its opposite interior angles.
If the exterior angle of a triangle is 90°, then what would be the opposite interior angles, supplementary or complementary?
How would you define an exterior angle property of a triangle?
An exterior angle of a triangle is equal to sum of opposite interior angles.
If the sum of interior opposite angles of a triangle is 130°, then what would be the measure of its exterior angle?
Sum of interior opposite angles = Exterior angle Exterior angle = 130°.
What is the angle form by straight line?
The straight line always form a angle of 180°.
What is the condition of exterior angle of a triangle?
The exterior angle of a triangle is equal to the sum of opposite interior angles.
What is the sum of exterior angles of a triangle?
We know that the sum of exterior angles of a polygon is always 360°. The sum of exterior angles of a triangle is 360°.
To verify that the exterior angle of a triangle is greater than either of its opposite interior angles.