Lines and Angles


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HD 13:55 Animated video Lecture for Lines and Angles

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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 3600 is called a complete angle. 
One quadrant  =  ¼ (Complete angle)
= 1/4 x 3600900 =
Two quadrants = 1/2 (Complete angle) = 1/2 x 3600 = 1800
Three quadrants=3/4
(Complete angle) = 3/4 x 3600 = 2700

Right angle:

An angle that measures 900 is called a right angle. A right angle makes a quarter revolutions.

Straight angle:

An angle that measures 1800 is called a straight angle. A straight angle makes a half revolution.

Acute angle:

An angle that measures less than 900 is called an acute angle.

Obtuse angle:

An angle that measures more than 900 and less than 1800 is called an obtuse angle.

Reflex angle:

An angle that measures more than 1800 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.

Questions & Answers

1 . Find the angle which is equal to twice its compliment
let the angle=x
then the complemet will be=(90-x)
2 . What do you mean by vertically opposite angles ?
Consider the lines AB and CD intersecting at point O as shown in the figure.

Here ∠AOC = ∠BOD and ∠AOD = ∠BOC are called ve...
3 . Find the bigger angle of the complementary angles.
Ratio of complementary angles is 3:7
Let the angles be 3x and 7x.
3x + 7x = 90°
10x = 90°
x = 9...
4 . Find the supplementary angle.
Supplementary angle of 100 o 30'
= 180° - 100 o  30'
= 79° 30'   
5 . Find the complementary angles.
Complementary angle of 50° 30'
= 90° – 50° 30'
= 39° 30'

Complementary angle of 20.5 o...