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anGLe 2. Name the arms, vertex and the angle so formed in each of the following figures.

When two rays or straight lines meet or intersect at a point, they form an angle. Also classify the angle.
(a) O (b) (c)
The rays forming the angle are called the arms of the angle. A P
C
The common point is called the vertex of the angle. A
Arm A B B Q
In the given figure, OA and OB are arms of the angle AOB. O is R

the vertex of the angle AOB. The vertex of the angle is always Angle
written in the middle. O Arm B oPen anD cLoseD fiGures
Vertex
Take an A4 sheet and fold it in half horizontally and mark the crease. Right Figures which have different

Then, fold the sheet in half vertically and mark the crease. Unfold the Angle starting and end points are
sheet and observe carefully. called open figures. Look at

We observe that both the creases intersect each other at a point and the given figures.

form an angle called a Right Angle. These all are open figures.

An angle less than a right is Right angle An angle more than a right Figures in which starting and end
angle an Acute angle. angle is an Obtuse angle. points coincide with each other are

D A P called closed figures. Look at the
given figures.

Acute angle Right angle Obtuse angle These are closed figures.
E F B C Q R
The closed figures or shapes
Also, the creases intersecting at a right angle represent perpendicular lines. which do not cross themselves
at any point are called simple
Think Tank Critical Thinking closed figures. Look at the given figures.
1. Where do you see angles around you?
2. I run side by side with my twin on two lines and never meet, no matter how far we go. What These are simple closed figures.
kind of lines are we running on?
3. When I meet another line, we form a perfect ‘L’. What are we called? PoLyGons

Simple closed figures made up of only line segments are called polygons. Look at
Practice time 7B the given figures.

1. Identify parallel, perpendicular and intersecting lines in the following figures.

(a) (b) (c) These are polygons.

types of Polygons

(d) (e) (f) A polygon is made up of three or more line segments called sides. A polygon is

identified as per the number of sides it has.

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