Class 9 Mathematics

Complete chapter-wise notes following NCERT curriculum with formulas and examples

Chapter 1: Number Systems

Learn about rational and irrational numbers, real numbers, their properties, representation on number line, and operations on real numbers.

Key Topics:

  • Introduction to Number Systems
  • Irrational Numbers
  • Real Numbers and Their Decimal Expansions
  • Representing Real Numbers on the Number Line
  • Operations on Real Numbers
  • Laws of Exponents for Real Numbers
  • Rationalization of Denominators
Important Formulas:
• √(ab) = √a × √b
• √(a/b) = √a / √b
• (√a + √b)(√a - √b) = a - b
• (a + √b)(a - √b) = a² - b
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Chapter 2: Polynomials

Understand polynomials in one variable, degree of polynomial, zeros of polynomial, remainder theorem, factorization, and algebraic identities.

Key Topics:

  • Introduction to Polynomials
  • Polynomials in One Variable
  • Zeros of a Polynomial
  • Remainder Theorem
  • Factor Theorem
  • Factorization of Polynomials
  • Algebraic Identities
Important Identities:
• (x + y)² = x² + 2xy + y²
• (x - y)² = x² - 2xy + y²
• x² - y² = (x + y)(x - y)
• (x + a)(x + b) = x² + (a+b)x + ab
• (x + y + z)² = x² + y² + z² + 2xy + 2yz + 2zx
• (x + y)³ = x³ + y³ + 3xy(x + y)
• x³ + y³ + z³ - 3xyz = (x+y+z)(x²+y²+z²-xy-yz-zx)
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Chapter 3: Coordinate Geometry

Introduction to Cartesian plane, plotting points, coordinates, quadrants, and finding distance between two points.

Key Topics:

  • Introduction to Coordinate Geometry
  • Cartesian System
  • Plotting Points in the Plane
  • Coordinates of a Point
  • Four Quadrants
  • Abscissa and Ordinate
  • Origin and Axes
Important Concepts:
• Point notation: P(x, y)
• Origin: O(0, 0)
• x-axis: y = 0
• y-axis: x = 0
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Chapter 4: Linear Equations in Two Variables

Solving linear equations with two variables, graphical representation of linear equations, and equations of lines parallel to axes.

Key Topics:

  • Introduction to Linear Equations
  • Linear Equations in Two Variables
  • Solution of a Linear Equation
  • Graph of a Linear Equation in Two Variables
  • Equations of Lines Parallel to x-axis and y-axis
Standard Forms:
• Linear equation: ax + by + c = 0
• Slope-intercept form: y = mx + c
• Two-point form: (y-y₁)/(y₂-y₁) = (x-x₁)/(x₂-x₁)
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Chapter 5: Introduction to Euclid's Geometry

Learn about Euclid's definitions, axioms, postulates, and the axiomatic approach to geometry.

Key Topics:

  • Introduction to Euclid's Geometry
  • Euclid's Definitions
  • Euclid's Axioms
  • Euclid's Postulates
  • Equivalent Versions of Euclid's Fifth Postulate
Euclid's Axioms (Examples):
• Things which are equal to the same thing are equal to one another
• If equals are added to equals, the wholes are equal
• If equals are subtracted from equals, remainders are equal
• The whole is greater than the part
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Chapter 6: Lines and Angles

Study types of angles, parallel lines, transversals, angle relationships, and theorems on angles.

Key Topics:

  • Basic Terms and Definitions
  • Intersecting Lines and Non-intersecting Lines
  • Pairs of Angles
  • Parallel Lines and a Transversal
  • Corresponding Angles
  • Alternate Interior Angles
  • Alternate Exterior Angles
  • Interior Angles on the Same Side of Transversal
  • Lines Parallel to the Same Line
  • Angle Sum Property of a Triangle
Important Results:
• Sum of angles in a triangle = 180°
• Linear pair of angles = 180°
• Vertically opposite angles are equal
• Corresponding angles are equal (parallel lines)
• Alternate interior angles are equal (parallel lines)
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Chapter 7: Triangles

Learn about congruence of triangles, criteria for congruence (SSS, SAS, ASA, RHS), properties of triangles, and inequalities in triangles.

Key Topics:

  • Introduction to Triangles
  • Congruence of Triangles
  • Criteria for Congruence of Triangles
  • SSS Congruence Rule
  • SAS Congruence Rule
  • ASA Congruence Rule
  • RHS Congruence Rule
  • Some Properties of a Triangle
  • Inequalities in a Triangle
Congruence Criteria:
• SSS: Side-Side-Side
• SAS: Side-Angle-Side
• ASA: Angle-Side-Angle
• AAS: Angle-Angle-Side
• RHS: Right angle-Hypotenuse-Side
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Chapter 8: Quadrilaterals

Study properties of parallelograms, rectangles, rhombus, squares, trapeziums, and the mid-point theorem.

Key Topics:

  • Introduction to Quadrilaterals
  • Angle Sum Property of a Quadrilateral
  • Types of Quadrilaterals
  • Properties of a Parallelogram
  • Another Condition for a Quadrilateral to be a Parallelogram
  • The Mid-point Theorem
  • Properties of Rectangle
  • Properties of Rhombus
  • Properties of Square
  • Properties of Trapezium
Important Properties:
• Sum of angles in a quadrilateral = 360°
• Opposite sides of parallelogram are equal
• Opposite angles of parallelogram are equal
• Diagonals of rectangle are equal
• Diagonals of rhombus bisect at right angles
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Chapter 9: Areas of Parallelograms and Triangles

Learn about areas of parallelograms and triangles on the same base and between the same parallels.

Key Topics:

  • Introduction to Areas
  • Figures on the Same Base and Between the Same Parallels
  • Parallelograms on the Same Base and Between the Same Parallels
  • Triangles on the Same Base and Between the Same Parallels
  • Relationship Between Area of Parallelogram and Triangle
Important Results:
• Area of parallelogram = base × height
• Area of triangle = ½ × base × height
• Triangles on same base and between same parallels are equal in area
• Area of triangle = ½ × area of parallelogram (same base & parallels)
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Chapter 10: Circles

Study circle properties, chords, arcs, angles subtended by chords, cyclic quadrilaterals, and circle theorems.

Key Topics:

  • Introduction to Circles
  • Chords of a Circle
  • Equal Chords and Their Distances from the Centre
  • Angle Subtended by an Arc of a Circle
  • Angle Subtended by a Chord at a Point
  • Cyclic Quadrilaterals
  • Perpendicular from the Centre to a Chord
Circle Theorems:
• Equal chords are equidistant from centre
• Angle in a semicircle is a right angle
• Angles in the same segment are equal
• Opposite angles of cyclic quadrilateral = 180°
• Perpendicular from centre bisects the chord
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Chapter 11: Constructions

Learn geometric constructions using compass and ruler - bisecting angles, perpendiculars, and constructing triangles.

Key Topics:

  • Introduction to Constructions
  • Basic Constructions
  • Construction of Bisector of a Line Segment
  • Construction of Bisector of an Angle
  • Construction of Perpendicular Lines
  • Construction of an Angle Equal to a Given Angle
  • Some Constructions of Triangles
  • Construction of Triangle Given Base, Base Angle and Sum of Other Two Sides
  • Construction of Triangle Given Base, Base Angle and Difference of Other Two Sides
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Chapter 12: Heron's Formula

Application of Heron's formula to find area of triangles and quadrilaterals when sides are given.

Key Topics:

  • Introduction to Heron's Formula
  • Area of a Triangle - by Heron's Formula
  • Application of Heron's Formula in Finding Areas of Quadrilaterals
Heron's Formula:
• Area of triangle = √[s(s-a)(s-b)(s-c)]
• where s = (a+b+c)/2 (semi-perimeter)
• a, b, c are the sides of triangle
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Chapter 13: Surface Areas and Volumes

Calculate surface area and volume of cubes, cuboids, cylinders, cones, spheres, and hemispheres.

Key Topics:

  • Introduction to Surface Areas and Volumes
  • Surface Area of a Cuboid and a Cube
  • Surface Area of a Right Circular Cylinder
  • Surface Area of a Right Circular Cone
  • Surface Area of a Sphere
  • Volume of a Cuboid
  • Volume of a Cylinder
  • Volume of a Right Circular Cone
  • Volume of a Sphere
  • Volume of a Hemisphere
Important Formulas:
Cuboid: TSA = 2(lb+bh+hl), Volume = l×b×h
Cube: TSA = 6a², Volume = a³
Cylinder: CSA = 2πrh, TSA = 2πr(r+h), Volume = πr²h
Cone: CSA = πrl, TSA = πr(l+r), Volume = ⅓πr²h
Sphere: SA = 4πr², Volume = 4/3πr³
Hemisphere: CSA = 2πr², TSA = 3πr², Volume = 2/3πr³
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Chapter 14: Statistics

Collection and presentation of data, mean, median, mode, graphical representation of data, and frequency distribution.

Key Topics:

  • Introduction to Statistics
  • Collection of Data
  • Presentation of Data
  • Graphical Representation of Data
  • Bar Graphs
  • Histograms
  • Frequency Polygons
  • Measures of Central Tendency
  • Mean (Arithmetic Mean)
  • Median
  • Mode
Formulas:
• Mean = Sum of observations / Number of observations
• Median = Middle value when arranged in order
• Mode = Most frequently occurring value
• Range = Highest value - Lowest value
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Chapter 15: Probability

Introduction to probability, experimental and theoretical probability, random experiments, outcomes, and events.

Key Topics:

  • Introduction to Probability
  • Random Experiments
  • Outcomes and Events
  • Experimental Probability
  • Theoretical Probability
  • Probability of an Event
  • Equally Likely Outcomes
  • Complementary Events
Basic Formulas:
• Probability of event E: P(E) = Number of favorable outcomes / Total number of outcomes
• 0 ≤ P(E) ≤ 1
• P(sure event) = 1
• P(impossible event) = 0
• P(not E) = 1 - P(E)
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