Subject

Maths

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Class -V

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Topic

Types of Angles

Competency

Understanding of Basic Concepts

ANGLES

ANGLES 1

• ANGLE1 looks like letter L these types of angles are called RIGHT ANGLE.

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• Its measure is 90 .

Angle 2

• Angle 2-measrment of angle 2 is less than
• 90 . These types of angle are called
• ACUTE ANGLE .

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ANGLE 3

• ANGLE 3- Measure of angle 3 is more than 90 .

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• These types of angle are called obtuse angles.

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LOOK AT THE ANGLES MARKED IN PICTURE �&�CIRCLE THE NAMES OF CORRECT ANGLE

• ANGLE NAMES

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A / O / R

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A / O / R

STOP

TICK THE NAMES OF ANGLES MARKED IN THE PICTURE

< 1 = A \ O \ R

< 2 = A \ O \ R

< 3 = A \ O \ R

< 4 = A \ O \ R

< 5 = A \ O \ R

TICK THE RIGHT ANSWER

• 1) 1 OF RIGHT ANGLE= ACUTE \ OBTUSE \ RIGHT ANGLE

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2) 20 less than right angle = ACUTE / OBTUSE / RIGHT ANGLE

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3) 20 more than right angle = ACUTE / OBTUSE / RIGHT ANGLE

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4)ACUTE ANGLE = MORE / LESS THAN 90*

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5)OBTUSE ANGLE = MORE / LESS THAN 90*

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THEREFORE ,�THERE ARE 3 TYPES ANGLES

RIGHT ACUTE OBTUSE

ANGLE ANGLE ANGLE

* LOOKS LIKE LETTER * MEASURE LESS * MEASURE MORE

L THAN 90* THAN 90*

Introduction based upon previous Knowledge

Q1. How angle Is formed ?

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Q2. Name the Vertex ?

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Q3. Name the arms of the angle ?

• Two rays with same initial point forms an angle

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Divider Clock Elbow joint

The angles are classified on the basis of their degree of measurement

An angle whose measure is greater than 0° and less than 90° is called an acute angle

An angle whose measure is 90° is called a right angle

Ex. 3 o’ Clock ,9 o’ Clock Hands of the clock make the right angle

An angle whose measure is greater than than 90 degree and less than 180 degree is called an obtuse angle

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• An angle whose measure is 180 Degree called straight angle.

Evaluation – Work Sheet

• Match the following

Straight Angle

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Acute Angle

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Obtuse Angle

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Right Angle

Identify the angles as right angle, acute, Obtuse and straight angle

A) 40 °

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B) 159 °

C) 90 °

D) 61 °

E) 180 °

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Acute angle

Obtuse angle

Right angle

Acute angle

Straight angle

50°

THE STANDARD UNIT FOR MEASURING AN ANGLE IS DEGREE.

To find the number of degrees in an angle, we use an instrument called protractor.

We can read the protractor from left to right or right to left.There are two semicircular scales on it. One contains 0° to 180°in anticlockwise direction called the inner scale and other contains 0° to 180° in clockwise direction called the outer scale. Each subdivision represents 1°.

65°

Calculate ‘X’ in the following

55°

X

45°

40°

X

X =

150°

X =

X =

35°

95°

X

5. COMPLETE ANGLE :An angle whose measure is 360° is called a complete angle.

6. REFLEX ANGLE : An angle whose measure is more than 180° but less than 360° is called a reflex angle.

ACUTE ANGLE

ACUTE ANGLE

OBTUSE ANGLE

RIGHT ANGLE

STRAIGHT ANGLE

OBTUSE ANGLE

Look at the clock hands and say what kind of angle they are forming.

A

B

O

The initial point O is called the VERTEX and

The two rays OA AND OB are called the ARMS or SIDES of the angle.

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Name the angles in each of the following figures:

O

P

Q

A

C

B

X

Y

Z

While naming an angle, the name of the vertex is always written in the middle.

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·

·

·

·

·

·

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Name the vertex and arms in each of the angles.

ARMS :

VERTEX :

VERTEX :

ARMS :

L

N

M

R

S

T

ML MN

M

S

SR ST

L

M

N

P

X

Y

Z

W

V

3 angles

6 angles

Angles are classified on the basis of their degree of measurement.

1.ACUTE ANGLE : An angle whose measure is between

and 90° is called an acute angle.

2.RIGHT ANGLE : An angle whose measure is 90° is called an right angle.

3. OBTUSE ANGLE :An angle whose measure is between 90° and 180° is called an obtuse angle.

4. STRAIGHT ANGLE : An angle whose measure is 180° is called a straight angle.