Page 142 - Math Skill - 4
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140                                                                                                  Maths


        Angle
        When two rays, lines or line segments meet at a point, an angle is formed.                 Arm          Y

        In the given figure, two rays OX      and OY  meet at a point
        O  and  an  angle  is  formed  at  their  meeting  point.  The                Vertex
        point where these rays meet is called the vertex and the                                    Arm
        rays form the arms of the angle.                                               O                          X

        An angle is denoted by the symbol ‘∠’. An angle is given its name in two ways:
          (i) Using a single capital letter at the vertex such as ∠O.
          (ii)  Using three capital letters with the vertex in the middle such as ∠XOY or ∠YOX.

        Interior and Exterior of an Angle                                                                  R

        The inside of an angle, that is, the region between the rays, is called                            A

        the interior of the angle. The points of the plane that do not lie on                    E
        the arms or in the interior of the angle lie to exterior of the angle.

        Look at the figure below.                                                                   B        C
        The points A, B and C are lying in the interior of the angle ∠PQR.              Q                         P
        Points D and E are lying in the exterior of the angle ∠PQR.                                 D



                                                    Exercise 10.2



          1. Identify the following as closed figures or open figures.








                   (a)            (b)            (c)           (d)            (e)           (f)            (g)

          2. Which of the following are polygons?

              (a)                          (b)                      (c)                      (d)






          3. Fill in the blanks.
              (a)  Figures that start and end at the same point are called ________.

              (b)  A point where two rays meet is called a ________.
              (c)  A polygon formed by 6 line segments is called a ________.

              (d)  A pentagon has ________ sides and ________ vertices.
              (e)  A heptagon has ________ sides and ________ vertices.
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