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SAI International School

                                                      CLASS – VII

           Mathematics

           Chapter-6: Triangle and its properties-2
           Lesson Notes - 2

           SUBTOPIC: Exterior angle and Angle sum property of a triangle



           SUBTOPICS: Exterior angle of a triangle and its property, angle sum property of a
           triangle:

           The Exterior Angle of a Triangle:


                 If we extend any side of the triangle then we get an exterior angle.
                 An exterior angle must form a linear pair with one of the interior angles of the triangle.
                 There are only two exterior angles possible at each of the vertices.


           Exterior angle property of a triangle

           STATEMENT: An Exterior angle of a triangle will always be equal to the sum of the two
           opposite interior angles of the triangle.



















           In the given figure, ∠1+∠2=∠3.

           This is called the Exterior angle property of a triangle.


           Example: Find the value of the unknown exterior angle x in the following diagram.
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