# NCERT Exemplar Solutions for Class 9 Maths Chapter 6 - Lines and Angles

## NCERT Exemplar Solutions Class 9 Maths Chapter 6 – Free PDF Download

NCERT Exemplar Solutions Class 9 Mathematics Chapter 6 Lines and Angles are provided in PDF for students to prepare for the annual exam. Our subject experts have designed exemplar problems in accordance with the latest CBSE syllabus (2023-2024) for Class 9, which covers the following topics of Chapter 6, Lines and Angles:

• Basic terms like line-segment, collinear points, non-collinear points, right angle, straight angle, acute angle, reflex angle, complementary angles, etc.
• Lines which are intersecting and non-intersecting
• Linear pair of angles such as adjacent angles, vertically opposite angles, etc.
• Transversal intersecting parallel lines, forming angles such as exterior angles and consecutive interior angles.
• Lines parallel to the same line
• Angle sum property of a triangle

This chapter is divided into two parts, and in the first part, the students will learn about lines, and in the second part, they will learn about different angles. Learning the concepts of Lines and Angles is very much important to understand the concepts of geometry in Class 9 as well as in Class 10. To make them understand these concepts effectively, a free PDF of the NCERT Exemplar Class 9 Maths are provided below.

## NCERT Exemplar Solutions for Class 9 Maths Chapter 6 Lines and Angles

### Access Answers to NCERT Exemplar Solutions for Class 9 Maths Chapter 6 Lines and Angles

Exercise 6.1 Page No: 55

Write the correct answer in each of the following:

1. In Fig. 6.1, if AB || CD || EF, PQ || RS, âˆ RQD = 25Â° and âˆ CQP = 60Â°, then âˆ QRS is equal to

(A) 85Â°

(B) 135Â°

(C) 145Â°

(D) 110Â°

Solution:

(C) 145Â°

Explanation:

According to the given figure, we have

AB || CD || EF

PQ || RS

âˆ RQD = 25Â°

âˆ CQP = 60Â°

PQ || RS.

We know that,

If a transversal intersects two parallel lines, then each pair of alternate exterior angles is equal.

Now, since PQ || RS

â‡’Â âˆ PQC =Â âˆ BRS

We haveÂ âˆ PQC = 60Â°

â‡’Â âˆ BRS = 60Â° â€¦ eq.(i)

We also know that,

If a transversal intersects two parallel lines, then each pair of alternate interior angles is equal.

Now again, since AB || CD

â‡’Â âˆ DQR =Â âˆ QRA

We haveÂ âˆ DQR = 25Â°

â‡’Â âˆ QRA = 25Â° â€¦ eq.(ii)

Using linear pair axiom,

We get,

âˆ ARS +Â âˆ BRS = 180Â°

â‡’Â âˆ ARS = 180Â° –Â âˆ BRS

â‡’Â âˆ ARS = 180Â° – 60Â° (From (i),Â âˆ BRS = 60Â°)

â‡’Â âˆ ARS = 120Â° â€¦ eq.(iii)

Now,Â âˆ QRS =Â âˆ QRA +Â âˆ ARS

From equations (ii) and (iii), we have,

âˆ QRA = 25Â° andÂ âˆ ARS = 120Â°

Hence, the above equation can be written as:

âˆ QRS = 25Â° + 120Â°

â‡’Â âˆ QRS = 145Â°

Therefore, option (C) is the correct answer.

2. If one angle of a triangle is equal to the sum of the other two angles, then the triangle is

(A) An isosceles triangle

(B) An obtuse triangle

(C) An equilateral triangle

(D) A right triangle

Solution:

(D) A right triangle

Explanation:

Let the angles of â–³ABC be âˆ A, âˆ B and âˆ C

Given that âˆ A= âˆ B+âˆ C â€¦(eq1)

But, in any â–³ABC,

Using the angle sum property, we have,

âˆ A+âˆ B+âˆ C=180o â€¦(eq2)

From equations (eq1) and (eq2), we get

âˆ A+âˆ A=180o

â‡’2âˆ A=180o

â‡’âˆ A=180o/2 = 90o

â‡’âˆ A = 90o

Hence, we get that the triangle is a right triangle

Therefore, option (D) is the correct answer.

3. An exterior angle of a triangle is 105Â°, and its two interior opposite angles are equal. Each of these equal angles is

(A) 37 Â½o

(B) 52 Â½o

(C) 72 Â½o

(D) 75Â°

Solution:

(B) 52 Â½o

Explanation:

According to the question,

The exterior angle of triangle = 105Â°

Let the two interior opposite angles of the triangle = x

We know that,

The exterior angle of a triangle = sum of interior opposite angles

Then, we have the equation,

105Â° = x + x

2x = 105Â°

x = 52.5Â°

x = 52Â½

Therefore, option (B) is the correct answer.

4. The angles of a triangle are in the ratio 5 : 3 : 7. The triangle is

(A) An acute angled triangle

(B) An obtuse-angled triangle

(C) A right triangle

(D) An isosceles triangle

Solution:

(A) An acute angled triangle

Explanation:

According to the question,

The angles of a triangle are of the ratio 5 : 3 : 7

Let 5:3:7 be 5x, 3x and 7x

Using the angle sum property of a triangle,

5x + 3x +7x =180

15x=180

x=12

Substituting the value of x, x = 12, in 5x, 3x and 7x we get,

5x = 5Ã—12 = 60o

3x = 3Ã—12 = 36o

7x = 7Ã—12 = 84o

Since all the angles are less than 90o, the triangle is an acute-angled triangle.

Therefore, option (A) is the correct answer.

Exercise 6.2 Page No: 56

1. For what value of x + y in Fig. 6.4 will ABC be a line? Justify your answer.

Solution:

The value of x + y should be 180o for ABC to be a line.

Justification:

From the figure, we can say that,

BD is a ray that intersects AB and BC at the point B, which results in

âˆ ABD = y

and,Â âˆ DBC = x

We know,

If a ray stands on a line, then the sum of two adjacent angles so formed is 180Â°.

â‡’Â If the sum of two adjacent angles is 180Â°, then a ray stands on a line.

Thus, for ABC to be a line,

The sum ofÂ âˆ ABD andÂ âˆ DBC should be equal to 180Â°.

â‡’Â âˆ ABD +Â âˆ DBC = 180Â°

â‡’Â x + y = 180Â°

Therefore, the value of x + y should be equal to 180Â° for ABC to be a line.

2. Can a triangle have all angles less than 60Â°? Give reasons for your answer.

Solution:

No. A triangle cannot have all angles less than 60Â°

Justification:

According to the angle sum property,

We know that the sum of all the interior angles of a triangle should be = 180o.

Suppose, all the angles are 60o,

Then we get, 60o + 60o + 60o = 180o.

Now, considering angles less than 60o,

Let us take 59o, which is the highest natural number less than 60o.

Then we have,

59o +59o + 59o = 177o â‰  180o

Hence, we can say that if all the angles are less than 60o, the measure of the angles wonâ€™t satisfy the angle sum property.

Therefore, a triangle cannot have all angles less than 60o.

3. Can a triangle have two obtuse angles? Give reasons for your answer.

Solution:

No. A triangle cannot have two obtuse angles

Justification:

According to the angle sum property,

We know that the sum of all the interior angles of a triangle should be = 180o.

An obtuse angle is one whose value is greater than 90Â° but less than 180Â°.

Considering two angles to be equal to the lowest natural number greater than 90o, i.e., 91o.

According to the question,

If the triangle has two obtuse angles, then there are two angles which are at least 91Â° each.

Sum of the two angles = 91Â° + 91Â°

â‡’ Sum of the two angles = 182Â°

The sum of these two angles already exceeds the sum of three angles of the triangle, even without considering the third angle.

Therefore, a triangle cannot have two obtuse angles.

4. How many triangles can be drawn having its angles as 45Â°, 64Â° and 72Â°? Give reasons for your answer.

Solution:

No triangle can be drawn having its angles 45Â°, 64Â° and 72Â°.

Justification:

According to the angle sum property,

We know that the sum of all the interior angles of a triangle should be = 180o.

But, according to the question,

We have the angles 45Â°, 64Â° and 72Â°.

Sum of these angles = 45Â° + 64Â° + 72Â°

= 181o, which is greater than 180o.

Hence, the angles do not satisfy the angle sum property of a triangle.

Therefore, no triangle can be drawn having its angles 45Â°, 64Â° and 72Â°.

5. How many triangles can be drawn having its angles as 53Â°, 64Â° and 63Â°? Give reasons for your answer.

Solution:

Infinitely many triangles can be drawn having its angles as 53Â°, 64Â° and 63Â°.

Justification:

According to the angle sum property,

We know that the sum of all the interior angles of a triangle should be = 180o.

According to the question,

We have the angles 53Â°, 64Â°, and 63Â°.

Sum of these angles = 53Â° + 64Â° + 63Â°

= 180o

Hence, the angles satisfy the angle sum property of a triangle.

Therefore, infinitely many triangles can be drawn having its angles as 53Â°, 64Â° and 63Â°.

Exercise 6.3 Page No: 58

1. In Fig. 6.9, OD is the bisector of âˆ AOC, OE is the bisector of âˆ BOC and OD âŠ¥ OE. Show that points A, O and B are collinear.

Solution:

According to the question,

In figure,

OD âŠ¥ OE,

OD and OE are the bisectors of âˆ AOC and âˆ BOC.

To prove: Points A, O and B are collinear

i.e., AOB is a straight line.

Proof:

Since OD and OE bisect angles âˆ AOC and âˆ BOC, respectively.

âˆ AOC = 2âˆ DOC â€¦(eq.1)

And âˆ COB = 2âˆ COE â€¦(eq.2)

Adding (eq.1) and (eq.2), we get

âˆ AOC = âˆ COB = 2âˆ DOC + 2âˆ COE

âˆ AOC +âˆ COB = 2(âˆ DOC +âˆ COE)

âˆ AOC + âˆ COB = 2âˆ DOE

Since, ODâŠ¥OE

We get,

âˆ AOC +âˆ COB = 2Ã—90o

âˆ AOC +âˆ COB =180o

âˆ AOB =180o

So, âˆ AOC + âˆ COB form linear pair.

Therefore, AOB is a straight line.

Hence, points A, O and B are collinear.

2. In Fig. 6.10, âˆ 1 = 60Â° and âˆ 6 = 120Â°. Show that the lines m and n are parallel.

Solution:

According to the question,

We have from the figure âˆ 1 = 60Â° and âˆ 6 = 120Â°

Since, âˆ 1 = 60Â° and âˆ 6 = 120Â°

Here, âˆ 1 = âˆ 3 [since they are vertically opposite angles]

âˆ 3 = âˆ 1 = 60Â°

Now, âˆ 3 + âˆ 6 = 60Â° + 120Â°

â‡’ âˆ 3 + âˆ 6 = 180Â°

We know that,

If the sum of two interior angles on the same side of l is 180Â°, then the lines are parallel.

Therefore, m || n

3. AP and BQ are the bisectors of the two alternate interior angles formed by the intersection of a transversal t with parallel lines l and m (Fig. 6.11). Show that AP || BQ.

Solution:

l || m and t is the transversal

âˆ MAB = âˆ SBA [alternate angles]

â‡’ Â½ âˆ MAB = Â½ âˆ SBA

â‡’ âˆ PAB = âˆ QBA

â‡’ âˆ 2 = âˆ 3

But, âˆ 2 and âˆ 3 are alternate angles.

Hence, AP||BQ.

4. If in Fig. 6.11, bisectors AP and BQ of the alternate interior angles are parallel, then show that l || m.

Solution:

AP is the bisector of âˆ MAB

BQ is the bisector of âˆ SBA.

Given: AP||BQ.

As AP||BQ,

We have,

So âˆ 2 = âˆ 3 [Alternate angles]

2âˆ 2 = 2âˆ 3

â‡’ âˆ 2 + âˆ 2 = âˆ 3 +âˆ 3

From figure, we have âˆ 1= âˆ 2and âˆ 3 = âˆ 4

â‡’ âˆ 1+ âˆ 2 = âˆ 3 +âˆ 4

â‡’ âˆ MAB = âˆ SBA

But, we know that these are alternate angles.

Hence, the lines l and m are parallel, i.e., l ||m.

5. In Fig. 6.12, BA || ED and BC || EF. Show that âˆ ABC = âˆ DEF [Hint: Produce DE to intersect BC at P (say)].

Solution:

Construction:

Extend DE to intersect BC at point, P.

Given, EF||BC and DP are the transversal,

âˆ DEF = âˆ DPC â€¦(eq.1) [Corresponding angles]

Also given, AB||DP and BC is the transversal,

âˆ DPC = âˆ ABC â€¦(eq.2) [Corresponding angles]

From (eq.1) and (eq.2), we get

âˆ ABC = âˆ DEF

Hence, Proved.

Exercise 6.4 Page No: 61

1. If two lines intersect, prove that the vertically opposite angles are equal.

Solution:

From the figure, we know that,

AB and CD intersect each other at point O.

Let the two pairs of vertically opposite angles be,

1stÂ pair –Â âˆ AOC andÂ âˆ BOD

2ndÂ pair –Â âˆ AOD andÂ âˆ BOC

To prove:

Vertically opposite angles are equal,

i.e., âˆ AOC =Â âˆ BOD, andÂ âˆ AOD =Â âˆ BOC

From the figure,

The ray AO stands on the line CD.

We know that,

If a ray lies on a line, then the sum of the adjacent angles is equal to 180Â°.

â‡’Â âˆ AOC +Â âˆ AOD = 180Â° (By linear pair axiom) â€¦ (i)

Similarly, the ray DO lies on line AOB.

â‡’Â âˆ AOD +Â âˆ BOD = 180Â° (By linear pair axiom) â€¦ (ii)

From equations (i) and (ii),

We have,

âˆ AOC +Â âˆ AOD =Â âˆ AOD +Â âˆ BOD

â‡’Â âˆ AOC =Â âˆ BOD – – – – (iii)

Similarly, the ray BO lies on the line COD.

â‡’Â âˆ DOB +Â âˆ COB = 180Â° (By linear pair axiom) – – – – (iv)

Also, the ray CO lies on line AOB.

â‡’Â âˆ COB +Â âˆ AOC = 180Â° (By linear pair axiom) – – – – (v)

From equations (iv) and (v),

We have,

âˆ DOB +Â âˆ COB =Â âˆ COB +Â âˆ AOC

â‡’Â âˆ DOB =Â âˆ AOC – – – – (vi)

Thus, from equation (iii) and equation (vi),

We have,

âˆ AOC =Â âˆ BOD, andÂ âˆ DOB =Â âˆ AOC

Therefore, we get vertically opposite angles are equal.

Hence Proved.

2. Bisectors of interior âˆ B and exterior âˆ ACD of a Î” ABC intersect at point T.

Prove that âˆ  BTC = Â½ âˆ  BAC.

Solution:

Given: â–³ ABC, produce BC to D, and the bisectors of âˆ ABC and âˆ ACD meet at point T.

To prove:

âˆ BTC = Â½ âˆ BAC

Proof:

In â–³ABC,âˆ ACD is an exterior angle.

We know that,

The exterior angle of a triangle is equal to the sum of two opposite angles,

Then,

âˆ ACD = âˆ ABC + âˆ CAB

Dividing L.H.S and R.H.S by 2,

â‡’ Â½ âˆ ACD = Â½ âˆ CAB + Â½ âˆ ABC

â‡’ âˆ TCD = Â½ âˆ CAB + Â½ âˆ ABC â€¦(1)

[âˆµCT is a bisector of âˆ ACDâ‡’ Â½ âˆ ACD = âˆ TCD]

We know that,

The exterior angle of a triangle is equal to the sum of two opposite angles,

Then in â–³ BTC,

âˆ TCD = âˆ BTC +âˆ CBT

â‡’ âˆ TCD = âˆ BTC + Â½ âˆ ABC â€¦(2)

[âˆµBT is the bisector of â–³ ABC â‡’âˆ CBT = Â½ âˆ ABC ]

From equations (1) and (2),

We get,

Â½ âˆ CAB + Â½ âˆ ABC = âˆ BTC + Â½ âˆ ABC

â‡’ Â½ âˆ CAB = âˆ BTC or Â½ âˆ BAC = âˆ BTC

Hence, proved.

3. A transversal intersects two parallel lines. Prove that the bisectors of any pair of corresponding angles so formed are parallel.

Solution:

Let,

ABÂ â•‘ CD

EF be the transversal passing through the two parallel lines at P and Q, respectively.

PR and QS are the bisectors ofÂ âˆ EPB and âˆ PQD.

We know that the corresponding angles of parallel lines are equal,

So, âˆ EPB = âˆ PQD

Â½ âˆ EPB = Â½ âˆ PQD

âˆ EPR = âˆ PQS

But, we also know that they are corresponding angles of PR and QS

Since the corresponding angles are equal,

We have,

PRÂ â•‘ QS

Hence Proved.

Students of Class 9 can use these exemplar solutions as a reference tool while practising the NCERT book exercise questions, which can also be downloaded in PDF form. Exemplar books, NCERT Solutions, notes and question papers are also provided at BYJU’S as study materials for students to learn and practise for their final exams.

Sample papers and previous years’ question papers will help students to know the question pattern and marks allotted for Chapter 6 of Class 9 Maths. Also, solve important questions with NCERT Exemplar for Chapter 6, Lines and Angles, by downloading the solutions in PDF, available in this article. Download BYJU’S – The Learning App to get personalised videos teaching various concepts of Maths, such as Lines and Angles and related topics, with the help of pictures and video animations.

## Frequently Asked Questions on NCERT Exemplar Solutions for Class 9 Maths Chapter 6

Q1

### What is the condition of collinearity of three points according to NCERT Exemplar Solutions for Class 9 Maths Chapter 6?

In general, lines can be parallel, perpendicular, intersection, etc. In all these cases, the slopes of lines are related to each other in some way. As we know, the slopes of two parallel lines are equal. If two lines have the same slope pass through a common point, these lines will coincide. In other words, if A, B, and C are three points in the XY-plane, they will lie on a line, i.e., three points are collinear if and only if the slope of AB is equal to the slope of BC.
Q2

### Mention the important topics covered in the NCERT Exemplar Solutions for Class 9 Maths Chapter 6.

The important topics covered in the NCERT Exemplar Solutions for Class 9 Maths Chapter 6 are listed below:
1. Basic terms like line-segment, collinear points, non-collinear points, right angle, straight angle, acute angle, reflex angle, complementary angles, etc.
2. Lines which are intersecting and non-intersecting
3. Linear pair of angles such as adjacent angles, vertically opposite angles, etc.
4. Transversal intersecting parallel lines forming angles such as exterior angles and consecutive interior angles.
5. Lines parallel to the same line
6. Angle sum property of a triangle
Q3

### What is meant by lines parallel to the same line covered in NCERT Exemplar Solutions for Class 9 Maths Chapter 6?

Lines that are parallel to the same line are parallel to each other. It means that if two lines are parallel to the same line, then they will be parallel to each other.