BASIC GEOMETRICAL IDEAS
POINT - A Point has no magnitude i.e. it has no length, breadth or thickness.
LINE - A Line is straight and extends indefinitely on both sides.
A
B
RAY - A Ray is part of a line, which has one end point, and extends indefinitely on the
other side.
P
Q
LINE SEGMENT – A part of a line is called a Line Segment.
R
S
PLANE – A Plane is a flat surface that extends indefinitely in all directions.
COLLINEAR POINTS – All points that lie on the same line are called Collinear Points.
OPEN AND CLOSED FIGURES
Open Figures – Figures that start from one point and end in another point are called
Open Figures.
Closed Figures – Figures that start from one point and end in the same point are called
Closed Figures.
INTERIOR AND EXTERIOR OF CLOSED FIGURES
EXTERIOR
Interior – The set of all points lying inside the closed figure is called the Interior of the
Closed Figures.
Exterior – The set of all points lying outside the closed figure is called the Exterior of
the Closed Figure.
Curvilinear Boundary – Shapes that have a curved shape have a Curvilinear Boundary
or Curvilinear Edge.
Linear Boundary – Shapes that are made up of straight lines have a Linear Boundary or
Linear Edge.
ANGLES
Angle – An Angle is formed by two rays starting from the same initial point.
A
(Arm)
(Vertex) O
(Arm)
B
Naming of an Angle –
(i). The symbol ‘ < ’ represents the Angle. The Vertex of the angle should always be
written in the middle. So, we can read the above angle as <AOB.
(ii). Sometimes an angle is named only by its Vertex, e.g. <O. It is read as Angle O.
(iii). We can also name an angle by a number 1,2,3… or a small letter a, b,c…
FORMING AN ANGLE
(i). An Angle is formed by two Rays starting from the same initial point.
(ii). It is also formed by two Line Segments having a common end point.
(iii). It is also formed by rotation of a Ray from an Initial position to a Terminal position.