Page 141 - New Medley 5 Semester 2

Plane and Lines

Plane

In our surroundings, we view a number of objects. Some of them have

smooth or flat surfaces and some have rough or curved surfaces. The
smooth surfaces like blackboard, tabletop, floor of the room, etc., come

close to the idea of a plane. A smooth surface is a part of a plane. A

plane has no certain definition, so we can say, “A plane has length and
breadth but no thickness. It is a flat surface that extends infinitely in all

directions.”
A
We generally represent a plane by a parallelogram

and marking three or more points, not in a line, with D B
it. Here is a plane ABCD.
C
Lines in a Plane

The two lines in a plane may either intersect at a point
A D
or not intersect at all however far, they are extended.

O
Here, the lines AB and CD intersect each other at a
C B
point O. These are called intersecting lines.

P Q
Here, the two lines PQ and RS never intesect at all.
R S
These are called parallel lines. is the symbol of

‘parallel to’. Thus, PQ RS is read as PQ is parallel to RS.
Angles

We see angles around us all the time. Observe the following things.

We observe that an angle is made by two rays originating from the same

point. This point is called vertex of the angle. The two rays that form an
angle are called its arms.

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