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# Lines and Angles

## Summary

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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° is called a complete angle.

One quadrant  =  $\frac{\text{1}}{\text{4}}$(complete angle) = $\frac{\text{1}}{\text{4}}$ x 360° = 90°

Two quadrants = $\frac{\text{1}}{\text{2}}$(complete angle) = $\frac{\text{1}}{\text{2}}$ x 360° = 180°

Three quadrants = $\frac{\text{3}}{\text{4}}$(complete angle) = $\frac{\text{3}}{\text{4}}$ x 360° = 270°

Right angle:
An angle that measures 90° is called a right angle. A right angle makes a quarter revolution.

Straight angle:
An angle that measures 180° is called a straight angle. A straight angle makes a half revolution.

Acute angle:
An angle that measures less than 90° is called an acute angle.

Obtuse angle:
An angle that measures more than 90° and less than 180° is called an obtuse angle.

Reflex angle:
An angle that measures more than 180° 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.

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