Class 9 Exam  >  Class 9 Notes  >  Lab Manuals for Class 9  >  Lab Manual: Verify that the Sum of the Angles of a Triangle is 180°

Lab Manual: Verify that the Sum of the Angles of a Triangle is 180° | Lab Manuals for Class 9 PDF Download

Objective

To verify that the sum of the angles of a triangle is 180°.

Materials Required
Cardboard sheet, White chart paper, Geometry box, Scissors, Adhesive, Drawing sheet, Tracing paper

Prerequisite Knowledge

  • Knowledge of straight angle
  • Concept of triangle and its properties

Theory

  • For straight line angle refer to Activity 11.
  • Triangle
    A plane figure closed by three intersecting lines is called a triangle, here Tri’ means ‘three’. A triangle has three sides, three angles and three vertices and it is denoted by the symbol ‘Δ’. A ΔABC is shown in Fig. 12.1.Lab Manual: Verify that the Sum of the Angles of a Triangle is 180° | Lab Manuals for Class 9

Some basic properties of triangles are given below:

  • The sum of all the angles of a triangle is always 180°.
  • Angles opposite to equal sides of a triangle are equal.
  • The sides opposite to equal angles in a triangle are equal.
  • In a triangle, the angle opposite to longer side is larger and vice-versa.
  • The sum of two sides of a triangle is greater than the third side.
  • The exterior opposite angle in a triangle is equal to sum of opposite interior angles.

Note: The property (1) is called Angle Sum Property of triangle.

Procedure

  • Take a cardboard of suitable size and by using adhesive, paste a white chart paper on it.
  • Draw a ΔABC of suitable lengths on the drawing sheet and also mark all the angles as shown in Fig. 12.2.
    Lab Manual: Verify that the Sum of the Angles of a Triangle is 180° | Lab Manuals for Class 9
  • By using tracing paper, cut out the angles respectively equal to ∠A , ∠B and ∠C from a drawing sheet, (see Fig. 12.3).
    Lab Manual: Verify that the Sum of the Angles of a Triangle is 180° | Lab Manuals for Class 9
  • Now, draw a line on the cardboard and paste the cut outs of the angles (∠A, ∠B and ∠C) on the line at a point O as shown in Fig. 12.4.
    Lab Manual: Verify that the Sum of the Angles of a Triangle is 180° | Lab Manuals for Class 9

Demonstration
When all the three cut outs of the angles A, B, C placed adjacent to each other at a point, then it forms a line forming a straight angle, i.e. 180°.
Flence, it is proved that the sum of the three angles of a triangle is 180°.
Therefore, ∠A + ∠B + ∠C =180°

Observation
Measure of ∠A = ………… ,
Measure of ∠B = ………… ,
Measure of ∠C = ………… ,
Hence, sum (∠A + ∠B + ∠C) = ………… .

Result
The sum of angles of a triangle is 180°, have been verified.

Application
This result can be used in many geometrical problems such as to find the sum of angles of a quadrilateral, pentagon and hexagon etc.

The document Lab Manual: Verify that the Sum of the Angles of a Triangle is 180° | Lab Manuals for Class 9 is a part of the Class 9 Course Lab Manuals for Class 9.
All you need of Class 9 at this link: Class 9
15 videos|98 docs

Top Courses for Class 9

15 videos|98 docs
Download as PDF
Explore Courses for Class 9 exam

Top Courses for Class 9

Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

Free

,

Sample Paper

,

Viva Questions

,

Extra Questions

,

Lab Manual: Verify that the Sum of the Angles of a Triangle is 180° | Lab Manuals for Class 9

,

video lectures

,

Exam

,

mock tests for examination

,

ppt

,

Objective type Questions

,

Important questions

,

study material

,

practice quizzes

,

Summary

,

pdf

,

past year papers

,

shortcuts and tricks

,

Lab Manual: Verify that the Sum of the Angles of a Triangle is 180° | Lab Manuals for Class 9

,

Semester Notes

,

Lab Manual: Verify that the Sum of the Angles of a Triangle is 180° | Lab Manuals for Class 9

,

Previous Year Questions with Solutions

,

MCQs

;