## 1. Summary

#### Length of a line segment:

The distance between the endpoints of a line segment is the **length** of the line segment. The length of a line segment can be measured accurately using a **ruler and a divider**.

#### Complete angle:

An angle of measure **360 ^{0}** is called a complete angle.

One quadrant = ¼ (Complete angle)

= 1/4 x 360

^{0}90

^{0}=

Two quadrants = 1/2 (Complete angle) = 1/2 x 360

^{0}= 180

^{0}

Three quadrants=3/4

(Complete angle) = 3/4 x 360

^{0}= 270

^{0}

#### Right angle:

An angle that measures **90 ^{0} **is called a right angle. A right angle makes

**a quarter revolutions**.

#### Straight angle:

An angle that measures **180 ^{0}** is called a straight angle. A straight angle makes

**a half revolution**.

#### Acute angle:

An angle that measures **less than 90 ^{0}** is called an acute angle.

#### Obtuse angle:

An angle that measures **more than 90 ^{0} and less than 180^{0}** is called an obtuse angle.

#### Reflex angle:

An angle that measures **more than 180 ^{0}** is called a reflex angle.

#### Intersecting lines:

Two lines that meet each other at a single point are called intersecting lines.

#### Perpendicular lines:

Two lines that **intersect each other at right angles** are said to be perpendicular to each other.

#### Bisector of a line segment:

A bisector of a line segment is a line that divides the line segment into **two equal parts**.

#### Perpendicular bisector of a line segment:

The perpendicular line that divides a line segment into two equal parts is called the perpendicular bisector of the line segment.