Understand angles and its types. click on the link to Watch the VIDEO explanation:
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Angles
When two straight lines meet at any point they form an angle.
In the figure OA and OB are called the arms of angle AOB.
The point at which the arms meet i.e. O is known as vertex of the angle.
The amount of turning from one arm to other is called the measure of the angle.
An angle is measured in degrees, minutes and seconds.
If a ray rotates about the starting initial position, in anticlockwise direction, as shown here notice that it comes back to its original position after 1 complete revolution, then we say that it has rotated to 3600 which implies that 1 complete rotation is divided into 360 equal parts. Each part is 10. 10 is divided into 60 equal parts and each part measures 1 minute. 1 minute is again divided into 60 equal parts and each part measures 1 second.
Kinds of Angles
The different kinds of angles are listed here
Acute angle : An angle whose measure is less than 900 is called an acute angle. For example using a protector measures 400 as shown here and mark a point. Join OB angle AOB = 400 which is less than a 900 and hence it is an acute angle.
Right Angle : An angle whose measure is 900 is called a right angle. For example using a protector measures 900 as shown here and mark a point. Join OB angle AOB is right angle since it is equal to 900
Obtuse angle : An angle whose measure is more than 900 and less than 1800 is called an Obtuse angle. For example using a protector measures 1350 as shown here and mark a point. Join OB angle AOB is Obtuse angle since it is equal to 1350 which is more than a 900 and less than a 1800 .
Straight Angle : An angle whose measure is 1800 is called a Straight angle.
Note: That a two right angles make a straight angles.
Reflex angle : An angle whose measure is more than 1800 and less than 3600 is called an Reflex angle. For example using a protector measures 2400 as shown here and mark a point. Join OB angle AOB is Reflex angle since it is equal to 2400 which is more than 1800 and less than 3600
Complete angle : An angle whose measure is 3600 is called a Complete angle.
Equal angle : Two angles are said to be equal, if they have the same measures. In the figure both the angles are equal to the 40 degrees and hence they are equal angles.
Adjacent angle : Two angles having a common vertex and a common arm, such that the other arms of these angles are on opposite sides of the common arm are called adjacent angles. In the figure O is the common vertex angle AOB and angle BOC are adjacent angles BO is the common arm.
Complementary angle : If the sum of the two angles is one right angle i.e. 90 degree, they are called Complementary angle. In the figure angle AOC plus angle COB is equal to 90 degree. Angle AOC is the complement of angle COB.
Supplementary angles : Two angles are said to be Supplementary, if the sum of their measures is 180 degree.
For example : Angles measuring 130 degree and 50 degree are Supplementary angles.
Two Supplementary angles are called the Supplement of each other.
Vertically opposite angles : When two straight lines intersect each other at a point, the pairs of opposite angles so formed are called vertically opposite angles.
Note : The Vertically opposite angles are always Equal. From the figure angle 4 equal to angle 2 and angle 1 equal to angle 3.
Bisector of an angle : If a ray or a straight line passing through the vertex of an angle, divides the angle in two angles of equal measurement then that line is known as Bisector of an angle. From the figure it is clear that angle BOC equals the angle COA and the ray OC is the bisector of the angle AOB.
Watch Video
Angles
When two straight lines meet at any point they form an angle.
In the figure OA and OB are called the arms of angle AOB.
The point at which the arms meet i.e. O is known as vertex of the angle.
The amount of turning from one arm to other is called the measure of the angle.
An angle is measured in degrees, minutes and seconds.
If a ray rotates about the starting initial position, in anticlockwise direction, as shown here notice that it comes back to its original position after 1 complete revolution, then we say that it has rotated to 3600 which implies that 1 complete rotation is divided into 360 equal parts. Each part is 10. 10 is divided into 60 equal parts and each part measures 1 minute. 1 minute is again divided into 60 equal parts and each part measures 1 second.
Kinds of Angles
The different kinds of angles are listed here
Acute angle : An angle whose measure is less than 900 is called an acute angle. For example using a protector measures 400 as shown here and mark a point. Join OB angle AOB = 400 which is less than a 900 and hence it is an acute angle.
Right Angle : An angle whose measure is 900 is called a right angle. For example using a protector measures 900 as shown here and mark a point. Join OB angle AOB is right angle since it is equal to 900
Obtuse angle : An angle whose measure is more than 900 and less than 1800 is called an Obtuse angle. For example using a protector measures 1350 as shown here and mark a point. Join OB angle AOB is Obtuse angle since it is equal to 1350 which is more than a 900 and less than a 1800 .
Straight Angle : An angle whose measure is 1800 is called a Straight angle.
Note: That a two right angles make a straight angles.
Reflex angle : An angle whose measure is more than 1800 and less than 3600 is called an Reflex angle. For example using a protector measures 2400 as shown here and mark a point. Join OB angle AOB is Reflex angle since it is equal to 2400 which is more than 1800 and less than 3600
Complete angle : An angle whose measure is 3600 is called a Complete angle.
Equal angle : Two angles are said to be equal, if they have the same measures. In the figure both the angles are equal to the 40 degrees and hence they are equal angles.
Adjacent angle : Two angles having a common vertex and a common arm, such that the other arms of these angles are on opposite sides of the common arm are called adjacent angles. In the figure O is the common vertex angle AOB and angle BOC are adjacent angles BO is the common arm.
Complementary angle : If the sum of the two angles is one right angle i.e. 90 degree, they are called Complementary angle. In the figure angle AOC plus angle COB is equal to 90 degree. Angle AOC is the complement of angle COB.
Supplementary angles : Two angles are said to be Supplementary, if the sum of their measures is 180 degree.
For example : Angles measuring 130 degree and 50 degree are Supplementary angles.
Two Supplementary angles are called the Supplement of each other.
Vertically opposite angles : When two straight lines intersect each other at a point, the pairs of opposite angles so formed are called vertically opposite angles.
Note : The Vertically opposite angles are always Equal. From the figure angle 4 equal to angle 2 and angle 1 equal to angle 3.
Bisector of an angle : If a ray or a straight line passing through the vertex of an angle, divides the angle in two angles of equal measurement then that line is known as Bisector of an angle. From the figure it is clear that angle BOC equals the angle COA and the ray OC is the bisector of the angle AOB.
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