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Math Concepts

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Comprehensive Class 9 Mathematics study notes designed for revision and exam preparation. Covers key concepts, formulas, worked examples, and chapter-wise summaries in a clear and easy-to-understand format to help students strengthen their understanding and practice effectively.

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GANITA MANJARI
Textbook of Mathematics for
GRADE

9
Part I

,0904 – G anita M anjari
ISBN 978-93-5729-603-8
Textbook of Mathematics for Grade 9 (Part I)

First Edition ALL RIGHTS RESERVED

April 2026 Chaitra 1948  No part of this publication may be reproduced, stored in a
retrieval system or transmitted, in any form or by any means,
electronic, mechanical, photocopying, recording or otherwise
without the prior permission of the publisher.
PD 2000T BS  This book is sold subject to the condition that it shall not, by
way of trade, be lent, re-sold, hired out or otherwise disposed
of without the publisher’s consent, in any form of binding or
© National Council of Educational cover other than that in which it is published.
Research and Training, 2026  The correct price of this publication is the price printed on
this page, Any revised price indicated by a rubber stamp or
by a sticker or by any other means is incorrect and should
be unacceptable.

OFFICES OF THE PUBLICATION
DIVISION, NCERT

NCERT Campus
Sri Aurobindo Marg
New Delhi 110 016 Phone : 011-26562708
108, 100 Feet Road
Hosdakere Halli Extension
Banashankari III Stage
Bengaluru 560 085 Phone : 080-26725740
Navjivan Trust Building
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Ahmedabad 380 014 Phone : 079-27541446
CWC Campus
Opp. Dhankal Bus Stop
Panihati
Kolkata 700 114 Phone : 033-25530454
115.00
CWC Complex
Maligaon
Guwahati 781 021 Phone : 0361-2674869



Publication Team

Head, Publication : M.V. Srinivasan
Division
Chief Editor : Bijnan Sutar
Chief Business Manager : Amitabh Kumar
Chief Production Officer : Deepak Jaiswal
Printed on 80 GSM paper with NCERT (In charge)
watermark Assistant Production : Prakash Veer Singh
Officer
Published at the Publication Cover
Division by the Secretary, National Akshita
Council of Educational Research
Layout
and Training, Sri Aurobindo Marg,
Bhuvan Enterprises
New Delhi 110016 and printed at
Krown Printers, B-20/1 (GF, FF, Illustrations
Akshita, Bhuvan Enterprises, and Ritika B
SF, Fourth Floor), Okhla Indl. Area,
Phase-2, New Delhi-110020

, Foreword
The National Education Policy (NEP) 2020 envisions an education system
that is firmly rooted in India’s cultural and intellectual wisdom, values, and
ethical traditions. The rich intellectual heritage simultaneously enables
learners to engage meaningfully with the complexities and possibilities of
a rapidly changing world. The National Curriculum Framework for School
Education (NCF-SE) 2023 provides concrete expression to this vision by laying
out a coherent curricular pathway across various stages of schooling that
nurtures critical thinking, creativity and sensitivity, along with the values and
dispositions that are needed for responsible citizenship in an interconnected
global society.
Learners have progressed through the Foundational, Preparatory and
Middle Stages, where their inherent potential has been nurtured holistically.
Now, they enter the Secondary Stage with enhanced capacity for reflection,
reasoning, enquiry, and self-expression. Spanning across Grades 9 to 12.
It marks a crucial period in the intellectual and personal growth of the students.
It prepares them to engage with abstract ideas, complex social realities, ethical
dilemmas and the expanding universe of knowledge, while deepening their
understanding of the self and the world around them.
The NCF-SE 2023 recommends that the curriculum for Grades 9–10 equips
students with the skills that are needed to grow as they advance in their lives.
Students can use these skills for reasoning, argumentation, and effective
communication. It endeavours to enhance their analytical and descriptive
capabilities to prepare them for the challenges and opportunities that await
them. A diverse curriculum, covering ten subjects: three languages — including
at least two languages native to India — Science, Mathematics, Social Sciences,
Arts Education, Physical Education and Well-being, Individuals in Society/
Environmental Education, Skill Education, and AI and Computational Thinking,
promotes their holistic development.
As per NCF-SE 2023, the Secondary Stage focuses on further developing
students’ ability to justify claims and arguments through logical reasoning.
At this stage, students are expected to be comfortable working with abstractions
and core techniques of Mathematics and Computational Thinking, such as
mathematical modelling and algorithm development for problem-solving. They
also need to strengthen key mathematical skills, including problem-solving,
visualisation, optimisation, representation, and communication, thereby
building essential capacities in Mathematics and Computational Thinking.
Engagement with puzzles, word problems, and optimisation tasks helps
nurture values and dispositiouns, such as perseverance, curiosity, confidence,
rigour and honesty.
The Grade 9 Mathematics textbook, Ganita Manjari (Part I), carries forward
the vision of NEP 2020 and NCF-SE 2023 by promoting mathematical thinking,
problem-solving skills, and intuition among students. Mathematical thinking
involves systematic and logical approaches to interpreting the world. This

, textbook aims to develop students’ ability in formulating well-defined problems
that can be addressed through mathematical reasoning — an essential aspect of
learning Mathematics. It also fosters mathematical intuition, enabling students
to develop a sense of what is likely to be true in Mathematics, which is a key
goal of school education.
This textbook marks an important transition from the Middle to the
Secondary Stage of Mathematics. While building on students’ prior experiences,
it introduces greater conceptual depth, formal reasoning, and the foundations
of proof. Through real-life examples and collaborative learning experiences, it
enhances creativity, logical reasoning, and decision-making skills. This textbook
also highlights the rich history of Mathematics in India, spanning thousands of
years. By learning about mathematical developments in India and across the
world, students can develop a deeper sense of cultural rootedness. The content
attempts to integrate mathematics with other subject areas such as science,
social science and with cross-cutting themes like environmental education,
value education and inclusive education. Additionally, the inclusion of
QR codes integrates technology, providing access to a variety of learning
resources.
The National Council of Educational Research and Training acknowledges
the contributions of the Textbook Development Team, subject experts,
pedagogues, practising teachers, reviewers, and all others who have supported
the development of this textbook. We hope Ganita Manjari inspires learners
to think critically, communicate with confidence, and engage thoughtfully in
society and the global community. We also warmly welcome suggestions and
feedback from all its users for further improvement in the subsequent editions.


Dinesh Prasad Saklani
Director
New Delhi National Council of Educational
April, 2026 Research and Training




iv

Índice general

  1. 01 Foreword 3
  2. 02 About the Book 5
  3. 03 National Syllabus and Teaching Learning Material Committee (NSTC) 9
  4. 04 CONSTITUTION OF INDIA 10
    1. Fundamental Rights 10
  5. 05 Textbook Development Team 11
  6. 06 Acknowledgements 13
  7. 07 Note to the Teacher 15
  8. 08 A Note to Students 17
  9. 09 Fundamental Duties 18
  10. 10 Ganita in India 20
  11. 11 Chapter 1: Orienting Yourself: The Use of Coordinates 21
    1. 1.1 Introduction 21
    2. 1.2 Settling In 22
    3. 1.3 The 2-d Cartesian Coordinate System 23
    4. 1.4 Distance Between Two Points in the 2-D Plane 28
  12. 12 Chapter 2: Introduction to Linear Polynomials 36
    1. 2.1 Introduction 36
    2. 2.2 Linear Polynomials 39
    3. 2.3 Exploring linear patterns 41
    4. 2.4 Linear growth and linear decay 44
    5. 2.5 Linear Relationships 46
    6. 2.6 Visualising linear relationships 47
  13. 13 Chapter 3: The World of Numbers 61
    1. 3.1 The Dawn of Mathematics: The Human Need to Count 61
    2. 3.1.1 A History Written in Bone 61
    3. 3.1.2 The Indian Context: Trade and Astronomy 62
    4. 3.2 The Revolution of Śhūnya: When Nothing Became Something 63
    5. 3.2.1 From Philosophy to Mathematics: The Concept of Śhūnya 63
    6. 3.2.2 The Bakhśhālī Manuscript and Brahmagupta's Rules 64
    7. 3.3 Integers: Expanding the Horizon 65
    8. 3.3.1 The Arithmetic of Integers 65
    9. 3.4 Filling the Spaces: Fractions and Rational Numbers 66
    10. 3.4.1 Representation of Rational Numbers on the Number Line 70
    11. 3.4.2 The Density of Rational Numbers 72
    12. 3.5 Irrational Numbers 73
    13. 3.5.1 The Proof of Irrationality of √2 73
    14. 3.5.2 Construction of Length 75
    15. 3.5.3 The Story of Pi (π) and Madhava's Infinite Series 76
    16. 3.6 Real Numbers: Decimals and Cyclic Patterns 77
    17. 3.6.1 Rational Decimals: Terminating and Repeating 77
    18. 3.6.2 The Magic of Cyclic Numbers 81
    19. 3.6.3 Irrational Decimals: Chaos and Infinity 81
    20. 3.7 Conclusion: The Never-Ending Journey 82
  14. 14 Chapter 4: Exploring Algebraic Identities 88
    1. 4.1 Introduction 88
    2. 4.2 Visualising Identities 89
    3. 4.3 Factorisation of Algebraic Expressions Using Identities 92
    4. 4.4 More Identities 95
    5. 4.5 Factorisation Using Algebra Tiles 98
    6. 4.6 Factorisation Without Using Algebra Tiles 100
    7. 4.7 Finding New Identities 102
    8. 4.8 Simplifying Rational Expressions 106
  15. 15 Chapter 5: I'm Up and Down, and Round and Round 112
    1. 5.1 Definitions 113
    2. 5.2 Symmetries of a Circle 114
    3. 5.3 How Many Circles? 114
    4. 5.4 Chords and the Angles They Subtend 118
    5. 5.5 Midpoints and Perpendicular Bisectors of Chords 120
    6. 5.6 Distance of Chords from the Centre 122
    7. 5.6.1 Which of the two unequal chords is farther from the centre? 124
    8. 5.7 Angles Subtended by an Arc 126
    9. 5.7.1 Angle subtended by an arc at a point on the circle 127
    10. 5.8 Concyclicity of Points 131
  16. 16 Chapter 6: Measuring Space: Perimeter and Area 138
    1. 6.1 Perimeter of a Shape 139
    2. 6.2 Perimeter of a Circle — The C/D Ratio 140
    3. 6.3 π Is Irrational 143
    4. 6.4 Length of an Arc of a Circle 145
    5. 6.5 Problems, Puzzles, and Paradoxes on Perimeter 147
    6. 6.6 Area of a Rectangle 150
    7. 6.7 Area of a Parallelogram 150
    8. 6.8 Area of a Triangle 152
    9. 6.8.1 Heron's formula 154
    10. 6.9 Squaring a Rectangle 160
    11. 6.10 Area of a Circle 163
    12. 6.10.1 Area of Sector of a Circle 166
  17. 17 Chapter 7: The Mathematics of Maybe: Introduction to Probability 175
    1. 7.1 What is Probability? 175
    2. 7.1.1 What is Randomness? 176
    3. 7.1.2 The Probability Scale 177
    4. 7.2 Measuring Probability Objectively 179
    5. 7.2.1 Experimental Probability: Performing Observations or Experiments 180
    6. 7.2.2 Theoretical Probability 181
    7. 7.2.3 Analysing Statistical Data Using Probability 182
    8. 7.3 Elements of Probability: Sample Spaces and Events 186
    9. 7.3.1 Sample Space 186
    10. 7.3.2 Events 187
    11. 7.4 Tree diagrams 188
  18. 18 Chapter 8: Predicting What Comes Next: Exploring Sequences and Progressions 194
    1. 8.1 Introduction to Sequences 194
    2. 8.2 Explicit Rule for a Sequence 196
    3. 8.3 Recursive Rule for a Sequence 198
    4. 8.4 Arithmetic Progressions 200
    5. 8.4.1 Visualising an AP 201
    6. 8.5 Sum of the First n Natural Numbers 203
    7. 8.6 Geometric Progressions 206
    8. 8.6.1 Fun with Fractals 208
    9. 8.6.2 Visualising a GP 210

Información del documento

Año escolar
4
Subido en
26 de junio de 2026
Número de páginas
220
Escrito en
2025/2026
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