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1.

Name the points :(i) in the interior of the angle PQR,(ii) in the exterior of the angle PQR.

Answer»

(i) a, b and x

(ii) d, m, n, s, and t.

2.

The measures of two supplementary angles are (3x + 15)° and (2x + 5)°. Find x.

Answer»

We know that, sum of two supplementary angles = 180°

∴ (3x + 15)° + (2x + 5)° = 180° ‘

3x + 15 + 2x + 5 = 180°

⇒ 3x + 2x + 15 + 5 = 180°

⇒ 5x°+ 20° = 180°

⇒ 5x = 180° – 20°

⇒ 5x = 160°

⇒ x = (160/5)°

⇒ x = 32°

3.

In the given figure, PQR is a straight line. Find x. Then complete the following:(i) ∠AQB = ……..(ii) ∠BQP = ……..(iii) ∠AQR = …….

Answer»

PQR is a straight line

∠AQP=x + 20°

∠AQB = 2x + 10°

∠BQR = x – 10°

But ∠AQP + ∠AQB + ∠BQR = 180°

⇒ x + 20° + 2x + 10° + x-10°= 180°

⇒ 4x + 20°= 180°

⇒ 4x= 180°- 20°= 160°

⇒ x = (160/4)° = 40°

(i) ∠AQB = 2x + 10° = 2 x 40° + 10° = 80° + 10° = 90°

∠AQP = x + 2(T = 40° + 20° = 60°)

∠BQR = x – 10° = 40° – 10° = 30°

(ii) ∠BQP = ∠AQP + ∠AQB = 60° + 90° = 150°

(iii) ∠AQR = ∠AQB + ∠BQR = 90° + 30° = 120°

4.

In the given diagram, ABC is a straight line.(i) If x = 53°, find y.(ii) If y =1 1/2 right angles ; find x.

Answer»

(i) From the figure,

∠ABD + ∠DBC = 180° (Linear pair of angles)

⇒ x + y = 180°

⇒ 53°+ y = 180° (∵ x = 53”)

⇒ y = 180° – 53°

⇒ y = 127°

(ii) From figure again,

x + y = 180°

1 + 3/2  x 90 = 180°

⇒ x + 1 1/2 right angles = 180°

⇒ x + 3/2 x 90 =180°

⇒ x + 135°= 180°

⇒ x = 180° – 135°

⇒ x = 45°

5.

Explain what do you understand by :(i) Adjacent angles ?(ii) Complementary angles ?(iii) Supplementary angles ?

Answer»

(i) Adjacent Angles: Two angles are called adjacent angles if (a) they have a common vertex (b) they have one common arm and (iii) the other two arms of the angles are on the opposite sides of the common arm.

(ii) Complementary Angles : Two angles whose sum is 90° are called complementary angles to each other.

(iii) supplementary angles:: Two angles whose sum.is 180° are called supplementary angles to each other.

6.

Two complementary angles are in the ratio 7 : 8. Find the angles.

Answer»

Let two complementary angles are 7x and 8x

∴ 7x + 8x = 90°

⇒ 15x = 90°

⇒ x = (90/15) °

⇒ x = 6°

∴ Two complementary angles are

7x = 7 x 6° = 42°

8x = 8 x 6° = 48°

7.

The measures of two complementary angles are (2x – 7)° and (x + 4)°. Find x.

Answer»

We know that, sum of two complementary angles = 90°

∴ (2x – 7) + (x + 4) = 90°

2x - 7 + x + 4 = 90°

⇒ 2x + x – 7 + 4 = 90°

⇒ 3x – 3 = 90°

⇒ 3x = 90 + 3

⇒ 3x = 93

⇒ x = 93/3

x = 31

8.

For an angle x°, find :(i) the complementary angle(ii) the supplementary angle(iii) the value of x° if its supplementary angle is three times its complementary angle.

Answer»

For an angle x,

(i) Complementary angle of x° = (90° – x)

(ii) Supplementary angle of x° = (180° – x)

(iii) ∵ ‘Supplementary angle = 3 (complementary anlge)

180°- x = 3 (90°-x)

⇒ 180°- x = 270°- 3x

⇒-x + 3x = 270°-180°

⇒ 2x = 90°

⇒x= (90/2)°= 45°

∴ x = 45°

9.

In the given figure; AB, CD and EF are straight lines. Name the pair of angles forming :(i) straight line angles.(ii) vertically opposite angles.

Answer»

In the given figure, AB, CD, and EF are straight lines on intersecting, angles are formed a, b, c, d, l, m, n, and p.

(i) In the figure pairs of straight line angles are ∠a, ∠b; ∠b, ∠c; ∠c, ∠d; ∠d, ∠a ∠l, ∠m; ∠m, ∠n;∠n, ∠p, and ∠p, ∠l

(ii) Pairs of vertical angles are ∠a, ∠c; ∠b, ∠d; ∠l, ∠n; ∠m, ∠p

10.

Example for obtuse angle.(1) 90°(2) 53°(3) 178°(4) 180°

Answer»

(3) 178° – Obtuse Angle

11.

Write the complement angle of :(i) 45°(ii) x°(iii) (x – 10)°(iv) 20° + y°

Answer»

(i) Complement angle of 45°

= 90° – 45° = 45°

(ii) Complement angle of x°

= 90° – x° = (90 – x)°

(iii) Complement angle of (x – 10)° = 90° (x – 10°)

= 90°- x + 10° = 100°-x

(iv) Complement angle of 20° + y°

= 90°- (20°+ y°)

= 90° – 20° -y° = 70° - y°

12.

Give two examples of parallel lines you can see in your environment.

Answer»

(i) Bars on the window.

(ii) Horizontal lines in the notebook are the examples of parallel lines.

13.

Give two examples of perpendicular lines you can see in your environment.

Answer»

(i) The angles formed by a pole and its shadow on the ground.

(ii) The adjacent sides of a notebook.

14.

Match the following:Measure of theangleType of the anglei. 180°a. Zero angleii. 240°b. Straight angleiii. 360°c. Reflex angleiv. 0°d. Complete angle

Answer»

Completed table:

 
Measure of the
angle
Type of the angle
i. 180°b. Straight angle
ii. 240°c. Reflex angle
iii. 360°d. Complete angle
iv. 0°a. Zero angle
15.

Say, true or false of the following:i. Parallel lines do not intersect each other.ii. Pole and its shadow on the ground makes a cute angle.iii. Angle between two parallel lines is 90°.iv. Angle between two intersecting lines may or may not be 90°.

Answer»

i. True

ii. False

iii. False

iv. True

16.

Complete the following table:AngleName of the angleVertex of the angleArts of the angle

Answer»
Sr. No.i.ii.iii.
Name of the angle∠PYR or ∠RYP∠LMN or ∠NML∠BOS or ∠SOB
Vertex of the angleYMO
Arms of the angleYP and YRML and MNOB and OS

17.

Look at the pictures below and identify the different types of angles.

Answer»

i. Complete angle 

ii. Reflex and Acute angle 

iii. Acute and Obtuse angle

18.

Look at the figures below and write the type of each of the angles:

Answer»

a. Acute angle 

b. Right angle 

c. Reflex angle 

d. Straight angle 

e. Zero angle 

f. Complete angle

19.

Measure the angles given below and write the measure in the given blanks. ......... ........ ......... . ...... .

Answer»

(1) 40° 

(2) 120° 

(3) 90° 

(4) 85°

20.

For each angle given below, write the name of the vertex, the names of the arms and the name of the angle.

Answer»

(i) In figure (i) O is the vertex, OA, OB is its arms and name of the angle is ∠AOB or∠BOA or simply ∠O.

(ii) In figure (ii) Q is the vertex, QP and QR its arms and the name of the angle is ∠PQR or ∠RQP or simply ∠Q.

(iii) In figure (iii), M is the vertex, MN and ML and its anus, and the name of the angle is ∠LMN or ∠NML or simply ∠M.

21.

Find the angle between minute hand and the hour hand of a clock when the time is 5.40.

Answer»

Angle described by the hour hand is 12 hours = 360° 

∴ per hour = 360°/12 = 30°

∴ Angle described in 5 hour 40 minutes i.e., in 17/3 x 30° = 170°

Now the angle described by minute hand is 60° minutes = 360° i.e., Angle in 40° minutes = 40 × 6° = 240°,

∴ Angle between the minutes hand to hour hand = 240° - 170° = 70° = (70° x π)/180 = 7π/18 radians

22.

Prove that tan α√(1 - sin2α) = sinα

Answer»

LHS : tanα √(1 - sin2α) = tanα √cos2α

= sinα/cosα x cosα = sinα = RHS

23.

Express 25°. 30′ 10″ in radians.

Answer»

25° + (1/2)° + (1/6)° = (150 + 3 + 1)/6 = 154/6 = 77°/3

⇒ 77/3 x π/180 = 77π/540 radians

24.

In the given figure, AOB is a straight line. Find the value of x and also answer each of the following :(i) ∠AOP = ……..(ii) ∠BOP = ……..(iii) which angle is obtuse ?(iv) which angle is acute ?

Answer»

∠AOP = x + 30°

∠BOP = x – 30°

But ∠AOP + ∠BOP = 180° (∵ ∠AOB is a straight angle)

⇒ x + 30°+ x - 30° = 180°

⇒ 2x = 180°

⇒ x = 90°

(i) ∠AOP = x + 30° = 90° + 30° = 120°

(ii) ∠BOP = x- 30° = 90° – 30° = 60°

(iii) ∠AOP is an obtuse angle

(iv) ∠BOP is an acute angle

25.

In the given figure ; AOC-is a straight line. If angle AOB = 50°, angle AOE = 90° and angle COD = 25° ; find the measure of :(i) angle BOC(ii) angle EOD(iii) obtuse angle BOD(iv) reflex angle BOD(v) reflex angle COE.

Answer»

(i) ∠AOB + ∠BOC = 180° (Linear pairs of angle)

⇒ 50° +∠BOC = 180°

⇒ ∠BOC = 180° – 50° = 130°

⇒ ∠BOC = 130°

(ii) ∠EOD + ∠COD = 90° (∵AOE = 90°)

⇒ ∠EOD + 25° = 90°

⇒ ∠EOD + 25° = 90°

⇒ ∠EOD = 90° – 25°

⇒ ∠EOD = 65°

(iii) ∠BOD = ∠BOC + COD

= 130° + 25° = 155°

(iv) Reflex ∠BOD = 360° – ∠BOD

= 360°- 155° = 205°

(v) Reflex ∠COE = 360° – ∠COE

= 360° (∠COD + ∠EOD)

= 360° – (25° + 65°)

= 360° – 90° = 270°

26.

In the given figure if :(i) a = 130° ; find b.(ii) b = 200 ; find a.(iii) a = 5/3 right angle, find b

Answer»

(i) From figure, 

a + b = 360°

⇒ 130° + 6 = 360

⇒ 6 = 360°-130°

⇒ b = 230°

(ii) From figure,

a + b = 360°

⇒ a + 200° = 360°

⇒ a = 360° – 200°

⇒ a = 160°

(iii) Here, a = 5/3 right angle

= 5/3 x 90° = 150°

a = 150°

Here, a + b = 360°

⇒ 150° + b = 360° (∵a = 150°)

⇒ b = 360° -150°

b = 210°

27.

If x = a cos θ + sin θ. y = a sin θ – b cos θ. Show that x2 + y2 = a2 + b2 

Answer»

Consider x2 = (acosθ + bsin θ)2 

⇒ x2 = a2cos2θ + 2abcosθsinθ + b2sin2θ …….(1) 

Again consider y2 = (asinθ – bcosθ)2 

⇒ y2 = a2sin2θ – abcosθ sinθ + b2cos2θ …….. (2) 

(1) + (2) ⇒ x2 + y2 = a2 + b2 

28.

Find the value of cos(π/3) – sin(π/6) – tan3(π/6)

Answer»

Now cos(π/3) - sin(π/6) - tan3(π/4)

= 1/2 - 1/2 - 13 - 1