Class IX Mathematics (Student Support Material 2025-26)

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Section A – Number Systems (Description)

The chapter Number Systems introduces students to different types of numbers used in mathematics and explains how they are related to each other. In basic mathematics, we begin with natural numbers, which are counting numbers starting from 1. When we include zero along with natural numbers, the set becomes whole numbers. When negative numbers are added to this set, we get integers.

Further, the concept of rational numbers is introduced. Rational numbers are numbers that can be written in the form p/q, where p and q are integers and q is not equal to zero. Examples include fractions such as ½, ¾, and decimals that either terminate or repeat.

However, not all numbers can be expressed as fractions. Numbers such as √2, √3, and π are called irrational numbers because their decimal expansions are non-terminating and non-repeating. When rational and irrational numbers are combined together, they form the set of real numbers. These numbers can be represented on the real number line.

Students also learn about decimal expansions and how rational numbers can have terminating or recurring decimals, while irrational numbers have non-terminating non-recurring decimals. Another important concept discussed in this section is the laws of exponents, which help simplify mathematical expressions involving powers.

Understanding number systems is important because it forms the foundation for advanced mathematics. Concepts such as algebra, geometry, and calculus rely heavily on the understanding of real numbers and their properties.

Questions for Section A

What are rational numbers and how are they represented?

Explain the difference between rational numbers and irrational numbers.

What are real numbers and how are they represented on a number line?

What is the difference between terminating and non-terminating decimals?

Write the laws of exponents used in real numbers.

Section B – Polynomials (Description)

A polynomial is an algebraic expression made up of variables, coefficients, and powers of variables combined using addition, subtraction, or multiplication. Examples of polynomials include expressions such as 4x³ – 3x + 7 or x² + 2x + 1. Polynomials are one of the most important concepts in algebra and are widely used in mathematics and science.

Polynomials can be classified in different ways. One method of classification is based on the number of terms present in the expression. A polynomial with one term is called a monomial, with two terms a binomial, and with three terms a trinomial.

Another way of classifying polynomials is based on their degree. The degree of a polynomial is the highest power of the variable present in the expression. For example, a polynomial with degree one is called a linear polynomial, degree two is called quadratic, and degree three is called cubic.

An important concept in this chapter is the zero of a polynomial. A zero of a polynomial is a value of the variable that makes the polynomial equal to zero. Students also learn about the remainder theorem and factor theorem, which are used to divide polynomials and determine their factors. These theorems are useful for solving algebraic equations and simplifying expressions.

The chapter also introduces algebraic identities, which are formulas used to expand or factorize algebraic expressions. Examples include
(a + b)² = a² + 2ab + b²
(a – b)² = a² – 2ab + b²
a² – b² = (a – b)(a + b)

These identities are extremely useful when simplifying expressions or solving equations.

Questions for Section B

What is a polynomial? Give examples.

Explain the different types of polynomials based on the number of terms.

What is the degree of a polynomial?

What do you mean by the zero of a polynomial?

Explain the remainder theorem and factor theorem.

Section C – Coordinate Geometry and Linear Equations (Description)

Coordinate geometry is a branch of mathematics that connects algebra with geometry. It helps us represent geometric figures using numbers and equations. In coordinate geometry, the position of a point is represented on a coordinate plane using two numbers called coordinates.

The coordinate plane consists of two perpendicular lines called the x-axis and y-axis. The point where these two axes intersect is called the origin, represented by (0,0). Every point on the plane can be represented using an ordered pair such as (x, y).

Students learn how to locate points on the coordinate plane and how to interpret graphs using coordinates. This concept is widely used in fields such as physics, engineering, economics, and computer science.

Another important concept included in this section is linear equations in two variables. A linear equation in two variables is an equation that can be written in the form ax + by + c = 0, where a, b, and c are constants. These equations represent straight lines when plotted on a graph.

Students learn how to find solutions to linear equations and represent them graphically. Each solution corresponds to a point on the line represented by the equation. Linear equations are used in many real-life applications such as calculating cost, distance, speed, and relationships between variables.