Mathematics Textbook for Class IX (2021-22) PDF

MATHEMATICS Textbook for Class IX 2021–22 0962 – MATHEMATICS ISBN 81-7450-489-3 Textbook for Class 9 First Edition ALL RIGHTS RESERVED February 200...

MATHEMATICS Textbook for Class IX 2021–22 0962 – MATHEMATICS ISBN 81-7450-489-3 Textbook for Class 9 First Edition ALL RIGHTS RESERVED February 2006 Phalguna 1927  No part of this publication may be reproduced, stored in a retrieval system Reprinted or transmitted, in any form or by any means, electronic, mechanical, October 2006 Kartika 1928 photocopying, recording or otherwise without the prior permission of the publisher. October 2007 Kartika 1929  This book is sold subject to the condition that it shall not, by way of January 2009 Magha 1930 trade, be lent, re-sold, hired out or otherwise disposed of without the January 2010 Pausa 1931 publisher’s consent, in any form of binding or cover other than that in January 2012 Magha 1933 which it is published. November 2012 Kartika 1934  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 October 2013 Kartika 1935 means is incorrect and should be unacceptable. December 2014 Pausa 1936 December 2015 Agrahayana 1937 December 2016 Pausa 1938 OFFICES OF THE PUBLICATION DIVISION, NCERT December 2017 Pausa 1939 December 2018 Agrahayana 1940 NCERT Campus Sri Aurobindo Marg August 2019 Shravana 1941 New Delhi 110 016 Phone : 011-26562708 January 2021 Pausa 1942 108, 100 Feet Road Hosdakere Halli Extension Banashankari III Stage PD 346T RSP Bangaluru 560 085 Phone : 080-26725740 © National Council of Educational Navjivan Trust Building P.O.Navjivan Research and Training, 2006 Ahmedabad 380 014 Phone : 079-27541446 CWC Campus Opp. Dhankal Bus Stop Panihati Kolkata 700 114 Phone : 033-25530454 CWC Complex Maligaon Guwahati 781 021 Phone : 0361-2674869 ` 155.00 Publication Team Head, Publication : Anup Kumar Rajput Division Chief Editor : Shveta Uppal Printed on 80 GSM paper with NCERT Chief Production Officer : Arun Chitkara watermark Chief Business : Vipin Dewan Manager (In charge) Published at the Publication Division by the Secretary, National Council of Editor : Bijnan Sutar Educational Research and Training, Sri Assistant Production : Mukesh Gaur Aurobindo Marg, New Delhi 110 016 Officer and printed at Pitambra Books Pvt. Cover and Illustrations Ltd., B-95, Industrial Area, Bijoli, Digital Expressions Jhansi- 284 135 (U.P.) 2021–22  FOREWORD The National Curriculum Framework (NCF), 2005, recommends that children’s life at school must be linked to their life outside the school. This principle marks a departure from the legacy of bookish learning which continues to shape our system and causes a gap between the school, home and community. The syllabi and textbooks developed on the basis of NCF signify an attempt to implement this basic idea. They also attempt to discourage rote learning and the maintenance of sharp boundaries between different subject areas. We hope these measures will take us significantly further in the direction of a child-centred system of education outlined in the national Policy on Education (1986). The success of this effort depends on the steps that school principals and teachers will take to encourage children to reflect on their own learning and to pursue imaginative activities and questions. We must recognize that, given space, time and freedom, children generate new knowledge by engaging with the information passed on to them by adults. Treating the prescribed textbook as the sole basis of examination is one of the key reasons why other resources and sites of learning are ignored. Inculcating creativity and initiative is possible if we perceive and treat children as participants in learning, not as receivers of a fixed body of knowledge. This aims imply considerable change is school routines and mode of functioning. Flexibility in the daily time-table is as necessary as rigour in implementing the annual calendar so that the required number of teaching days are actually devoted to teaching. The methods used for teaching and evaluation will also determine how effective this textbook proves for making children’s life at school a happy experience, rather then a source of stress or boredom. Syllabus designers have tried to address the problem of curricular burden by restructuring and reorienting knowledge at different stages with greater consideration for child psychology and the time available for teaching. The textbook attempts to enhance this endeavour by giving higher priority and space to opportunities for contemplation and wondering, discussion in small groups, and activities requiring hands-on experience. The National Council of Educational Research and Training (NCERT) appreciates the hard work done by the textbook development committee responsible for this book. We wish to thank the Chairperson of the advisory group in science and mathematics, Professor J.V. Narlikar and the Chief Advisor for this book, Professor P. Sinclair of IGNOU, New Delhi for guiding the work of this committee. Several teachers contributed 2021–22 to the development of this textbook; we are grateful to their principals for making this possible. We are indebted to the institutions and organizations which have generously permitted us to draw upon their resources, material and personnel. We are especially grateful to the members of the National Monitoring Committee, appointed by the Department of Secondary and Higher Education, Ministry of Human Resource Development under the Chairpersonship of Professor Mrinal Miri and Professor G.P. Deshpande, for their valuable time and contribution. As an organisation committed to systemic reform and continuous improvement in the quality of its products, NCERT welcomes comments and suggestions which will enable us to undertake further revision and refinement. Director New Delhi National Council of Educational 20 December 2005 Research and Training 2021–22  TEXTBOOK DEVELOPMENT COMMITTEE CHAIRPERSON, ADVISORY GROUP IN SCIENCE AND MATHEMATICS J.V. Narlikar, Emeritus Professor, Chairman, Advisory Committee, Inter University Centre for Astronomy & Astrophysics (IUCAA), Ganeshkhind, Pune University, Pune CHIEF ADVISOR P. Sinclair, Director, NCERT and Professor of Mathematics , IGNOU, New Delhi CHIEF COORDINATOR Hukum Singh, Professor (Retd.), DESM, NCERT MEMBERS A.K. Wazalwar, Professor and Head, DESM, NCERT Anjali Lal, PGT, DAV Public School, Sector-14, Gurgaon Anju Nirula, PGT, DAV Public School, Pushpanjali Enclave, Pitampura, Delhi G.P. Dikshit, Professor (Retd.), Department of Mathematics & Astronomy, Lucknow University, Lucknow K.A.S.S.V. Kameswara Rao, Associate Professor, Regional Institute of Education, Bhubaneswar Mahendra R. Gajare, TGT, Atul Vidyalya, Atul, Dist. Valsad Mahendra Shanker, Lecturer (S.G.) (Retd.), NCERT Rama Balaji, TGT, K.V., MEG & Centre, ST. John’s Road, Bangalore Sanjay Mudgal, Lecturer, CIET, NCERT Shashidhar Jagadeeshan, Teacher and Member, Governing Council, Centre for Learning, Bangalore S. Venkataraman, Lecturer, School of Sciences, IGNOU, New Delhi Uaday Singh, Lecturer, DESM, NCERT Ved Dudeja, Vice-Principal (Retd.), Govt. Girls Sec. School, Sainik Vihar, Delhi MEMBER-COORDINATOR Ram Avtar, Professor (Retd.), DESM, NCERT (till December 2005) R.P. Maurya, Professor, DESM, NCERT (Since January 2006) 2021–22  ACKNOWLEDGEMENTS The Council gratefully acknowledges the valuable contributions of the following participants of the Textbook Review Workshop: A.K. Saxena, Professor (Retd.), Lucknow University, Lucknow; Sunil Bajaj, HOD, SCERT, Gurgaon; K.L. Arya, Professor (Retd.), DESM, NCERT; Vandita Kalra, Lecturer, Sarvodaya Kanya Vidyalya, Vikas Puri, District Centre, New Delhi; Jagdish Singh, PGT, Sainik School, Kapurthala; P.K. Bagga, TGT, S.B.V. Subhash Nagar, New Delhi; R.C. Mahana, TGT, Kendriya Vidyalya, Sambalpur; D.R. Khandave, TGT, JNV, Dudhnoi, Goalpara; S.S. Chattopadhyay, Assistant Master, Bidhan Nagar Government High School, Kolkata; V.A. Sujatha, TGT, K.V. Vasco No. 1, Goa; Akila Sahadevan, TGT, K.V., Meenambakkam, Chennai; S.C. Rauto, TGT, Central School for Tibetans, Mussoorie; Sunil P. Xavier, TGT, JNV, Neriyamangalam, Ernakulam; Amit Bajaj, TGT, CRPF Public School, Rohini, Delhi; R.K. Pande, TGT, D.M. School, RIE, Bhopal; V. Madhavi, TGT, Sanskriti School, Chanakyapuri, New Delhi; G. Sri Hari Babu, TGT, JNV, Sirpur Kagaznagar, Adilabad; and R.K. Mishra, TGT, A.E.C. School, Narora. Special thanks are due to M. Chandra, Professor and Head (Retd.), DESM, NCERT for her support during the development of this book. The Council acknowledges the efforts of Computer Incharge, Deepak Kapoor; D.T.P. Operator, Naresh Kumar; Copy Editor, Pragati Bhardwaj; and Proof Reader, Yogita Sharma. Contribution of APC–Office, administration of DESM, Publication Department and Secretariat of NCERT is also duly acknowledged. 2021–22  CONTENTS FOREWORD iii 1. NUMBER SYSTEMS 1 1.1 Introduction 1 1.2 Irrational Numbers 5 1.3 Real Numbers and their Decimal Expansions 8 1.4 Representing Real Numbers on the Number Line 15 1.5 Operations on Real Numbers 18 1.6 Laws of Exponents for Real Numbers 24 1.7 Summary 27 2. POLYNOMIALS 28 2.1 Introduction 28 2.2 Polynomials in One Variable 28 2.3 Zeroes of a Polynomial 32 2.4 Remainder Theorem 35 2.5 Factorisation of Polynomials 40 2.6 Algebraic Identities 44 2.7 Summary 50 3. COORDINATE GEOMETRY 51 3.1 Introduction 51 3.2 Cartesian System 54 3.3 Plotting a Point in the Plane if its Coordinates are given 61 3.4 Summary 65 4. LINEAR EQUATIONS IN TWO VARIABLES 66 4.1 Introduction 66 4.2 Linear Equations 66 4.3 Solution of a Linear Equation 68 4.4 Graph of a Linear Equation in Two Variables 70 4.5 Equations of Lines Parallel to x-axis and y-axis 75 4.6 Summary 77 2021–22 5. INTRODUCTION TO EUCLID’S GEOMETRY 78 5.1 Introduction 78 5.2 Euclid’s Definitions, Axioms and Postulates 80 5.3 Equivalent Versions of Euclid’s Fifth Postulate 86 5.4 Summary 88 6. LINES AND ANGLES 89 6.1 Introduction 89 6.2 Basic Terms and Definitions 90 6.3 Intersecting Lines and Non-intersecting Lines 92 6.4 Pairs of Angles 92 6.5 Parallel Lines and a Transversal 98 6.6 Lines Parallel to the same Line 101 6.7 Angle Sum Property of a Triangle 105 6.8 Summary 108 7. TRIANGLES 109 7.1 Introduction 109 7.2 Congruence of Triangles 109 7.3 Criteria for Congruence of Triangles 112 7.4 Some Properties of a Triangle 120 7.5 Some More Criteria for Congruence of Triangles 125 7.6 Inequalities in a Triangle 129 7.7 Summary 134 8. QUADRILATERALS 135 8.1 Introduction 135 8.2 Angle Sum Property of a Quadrilateral 136 8.3 Types of Quadrilaterals 137 8.4 Properties of a Parallelogram 139 8.5 Another Condition for a Quadrilateral to be a Parallelogram 145 8.6 The Mid-point Theorem 148 8.7 Summary 151 9. AREAS OF PARALLELOGRAMS AND TRIANGLES 152 9.1 Introduction 152 9.2 Figures on the same Base and Between the same Parallels 154 2021–22  9.3 Parallelograms on the same Base and between the same Parallels 156 9.4 Triangles on the same Base and between the same Parallels 160 9.5 Summary 167 10. CIRCLES 168 10.1 Introduction 168 10.2 Circles and its Related Terms : A Review 169 10.3 Angle Subtended by a Chord at a Point 171 10.4 Perpendicular from the Centre to a Chord 173 10.5 Circle through Three Points 174 10.6 Equal Chords and their Distances from the Centre 176 10.7 Angle Subtended by an Arc of a Circle 179 10.8 Cyclic Quadrilaterals 182 10.9 Summary 187 11. CONSTRUCTIONS 187 11.1 Introduction 188 11.2 Basic Constructions 189 11.3 Some Constructions of Triangles 191 11.4 Summary 196 12. HERON’S FORMULA 197 12.1 Introduction 197 12.2 Area of a Triangle – by Heron’s Formula 199 12.3 Application of Heron’s Formula in finding Areas of Quadrilaterals 203 12.4 Summary 207 13. SURFACE AREAS AND VOLUMES 208 13.1 Introduction 208 13.2 Surface Area of a Cuboid and a Cube 208 13.3 Surface Area of a Right Circular Cylinder 214 13.4 Surface Area of a Right Circular Cone 217 13.5 Surface Area of a Sphere 222 13.6 Volume of a Cuboid 226 13.7 Volume of a Cylinder 228 2021–22  13.8 Volume of a Right Circular Cone 231 13.9 Volume of a Sphere 234 10.10 Summary 237 14. STATISTICS 238 14.1 Introduction 238 14.2 Collection of Data 239 14.3 Presentation of Data 240 14.4 Ggraphical Representation of Data 247 14.5 Measures of Central Tendency 261 14.6 Summary 270 15. PROBABILITY 271 15.1 Introduction 271 15.2 Probability – an Experimental Approach 272 15.3 Summary 285 APPENDIX – 1 PROOFS IN MATHEMATICS 286 A1.1 Introduction 286 A1.2 Mathematically Acceptable Statements 287 A1.3 Deductive Reasoning 290 A1.4 Theorems, Conjectures and Axioms 293 A1.5 What is a Mathematical Proof? 298 A1.6 Summary 305 APPENDIX – 2 INTRODUCTION TO MATHEMATICAL MODELLING 306 A2.1 Introduction 306 A2.2 Review of Word Problems 307 A2.3 Some Mathematical Models 311 A2.4 The Process of Modelling, its Advantages and Limitations 319 A2.5 Summary 322 ANSWERS/HINTS 325-350 2021–22