Page 157 - Start Up Mathematics_5

12

Lines, Angles and Triangles

Let's Recall …

• A point is just a dot made on paper. It has no shape or size. It is the smallest
geometrical shape. We denote a point by a capital letter.
A B K are some examples of points.

• When we take two points and join them using a scale, we
get a line segment. AB is a line segment. Its length can be A B
measured. A and B are called the two end points of AB.
• A line segment that extends on one side is called a ray. It has
one end point. Its other end can be extended indefinitely. A B
AB is a ray with A as its end point.

• A line segment that extends on both sides is called a line.
It has no end points. It is denoted as AB and cannot be A B
measured.
• Lines can be broadly categorized into two main types.

1. Straight lines 2. Curved lines

A A
Vertical Slanting Horizontal arm C
line B line B line A B

• When two rays meet at a common end point, an angle is formed. vertex angle
The common end point is called the vertex and the two rays are A B
called the arms of the angle. The angle shown in the figure is read
as ∠BAC or ∠CAB. P
• Angles are mainly of four types.
(a) An angle formed by a vertical line and a horizontal line is called
a right angle. ∠PQR is a right angle. Q R

P L
(b) An angle less than a right angle is called an acute angle.
∠LQR is an acute angle.

Q R
P

(c) An angle greater than a right angle is called an obtuse angle. M
∠MQR is an obtuse angle.
Q R

149