Page 156 - ICSE Math 6
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Line segment
A line segment is a part of a line from one fixed point to the other. A line segment has two end points
and a definite length. Given below is a line segment denoted by AB or BA.
A B
Although a line segment has a definite length, it consists of infinite number of points. The edges of a
ruler and the edges of a table are examples of line segments.
Ray
A ray is a part of a line which starts from a fixed point and moves endlessly in a direction. Given
−
→
below is a ray denoted by PQ .
P Q
An arrow on one side of a ray shows that the ray extends indefinitely in one direction only. A ray has
only one end point also known as its initial point. Two rays AB and AC having the same initial point
A and moving in opposite directions are known as opposite rays.
C A B
Plane
A plane is a flat surface. It has infinite length A
and breadth and hence extends infinitely. A M N p Maths Info
plane consists of infinite number of points R C The lines which lie in the same
and lines. It is denoted by small letters like p B Q plane are known as coplanar
or q or by three points (not in a straight line) Plane p or Plane ABC lines.
drawn on it.
Top of a table and surface of a sheet of paper are some examples of a plane.
Space
Space is a set containing innumerable points. Thus, all points, lines and planes belong to space.
Space has infinite length, breadth and height. For example, walls, floor, ceiling and the interior of a
room are part of space.
Parallel lines m
Two lines which lie in the same plane and do not meet even when extended l
indefinitely are known as parallel lines. The distance between two parallel lines
always remains the same. In the adjoining figure, lines l and m are parallel to each
other and are represented by l || m (read as l is parallel to m).
Intersecting lines
Two lines which lie in the same plane
and have a common point are known as l
intersecting lines. The common point is l
known as the point of intersection. In O O
the adjoining figures, lines l and m are m m
intersecting lines and O is their point of
intersection.
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