## RS Aggarwal Class 6 Math Thirteenth Chapter Angels And Their Measurement Exercise 13B Solution

## EXERCISE 13B

### Some Concepts About Angle

**Magnitude Angle:** *The magnitude of an angle is amount of rotation through which one of the arms must be rotated about the vertex to bring it to the position of the other.*

**Right Angle:** *A quarter turn of a ray OA about O describes an angle called a right angle. 1 right angle = 90 ^{o}*

#### VARIOUS TYPES OF ANGLES

**Acute Angle:** *An angle whose measure is more than 0 ^{o} but less than 90^{o} is called acute angle.*

**Right Angle:** *An angle whose measure is 90 ^{o }is called right angle.*

**Obtuse Angle:*** An angle whose measure is more than 90 ^{o} but less than 180^{o} is called an obtuse angle.*

**Straight Angle:** *An angle whose measure is 180 ^{o} is called a straight angle.*

**Reflex Angle:** *An angle whose measure is more than 180 ^{o} but less than 360^{o} is called a reflex angle.*

**Complete Angle: ***An angle whose measure is 360 ^{o} is called a complete angle.*

Zero **Angle:** *The angle whose measure is 0 ^{o} is called a zero angle.*

**(1) State the type of each of the following angles:**

Ans: (i) Obtuse angle

(ii) Right angle

(iii) Straight angle

(iv) Reflex angle

(v) acute angle

(vi) Complete angle

**(2) Classify the angles whose magnitudes are given below:**

(i) 30^{o }

Ans: Acute

(ii) 91^{o}

Ans: Obtuse

(iii) 179^{o}

Ans: Obtuse

(iv) 90^{o}

Ans: Right

(v) 181^{o}

Ans: Reflex

(vi) 360^{o}

Ans: Complete

(vii) 128^{o}

Ans: Obtuse

(viii) (90.5)^{o}

Ans: Obtuse

(ix) (38.3)^{o}

Ans: Acute

(x) 80^{o}

Ans: Acute

(xi) 0^{o}

Ans: Zero

(xii) 15^{o}

Ans: Acute

**(3) How many degrees are there in**

(i) One right angle?

Ans: 90^{o}

(ii) Two right angles?

Ans: 180^{o}

(iii) Three right angles?

Ans: 270^{o}

(iv) Four right angles?

Ans: 360^{o}

**(4) How many degrees are there in the angle between the hour hand and the minute hand of a clock, when it is**

(i) 3 o’clock

Ans: 90^{o}

(ii) 6 o’clock

Ans: 180^{o }

(iii) 12 o’clock

Ans: 0^{o}

(iv) 9 o’clock

Ans: 90^{o }

**(5) Using only a ruler, drawn an acute angle, an obtuse angle and a straight angle?**

(i) ∠AOB is an acute angle.

(ii) ∠POQ is an obtuse angle.

(iii) ∠XOY = 180 degree = a straight angle.

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