Unravel the mysteries of algebraic expressions and identities with our comprehensive Class 8 Mathematics notes.

Chapter 8: Algebraic Expressions and Identities

Chapter 8: Algebraic Expressions and Identities

Overview of the Chapter

Introduction to Algebraic Expressions

Definition: An algebraic expression is a mathematical phrase that can contain numbers, variables (like x or y), and operations (like addition, subtraction, multiplication, and division).

Example: 3x + 5 is an algebraic expression.

Terms, Factors, and Coefficients

Understanding Terms

Terms: The components of an algebraic expression separated by plus or minus signs are called terms.

Example: In the expression 3x + 5, 3x and 5 are terms.

Factors

Factors: The numbers or variables that multiply together to form a term are called factors.

Example: In the term 3x, 3 and x are factors.

Coefficients

Coefficient: The numerical factor of a term is called the coefficient.

Example: In the term 3x, 3 is the coefficient.

Types of Algebraic Expressions

Monomials, Binomials, and Polynomials

Monomial: An algebraic expression with only one term.

Example: 7xy is a monomial.

Binomial: An algebraic expression with two terms.

Example: a + b is a binomial.

Polynomial: An algebraic expression with more than one term.

Example: x² + 3x + 4 is a polynomial.

Addition and Subtraction of Algebraic Expressions

Combining Like Terms

Like Terms: Terms that have the same variables and powers are called like terms.

Example: 3x and 5x are like terms and can be combined to form 8x.

Addition/Subtraction: Only like terms can be added or subtracted.

Example: 3x + 4x = 7x.

Multiplication of Algebraic Expressions

Multiplication of Monomials

Monomial by Monomial: Multiply the coefficients and the variables separately.

Example: 3x × 4x = 12x².

Multiplication of a Monomial by a Polynomial

Monomial by Polynomial: Multiply each term of the polynomial by the monomial.

Example: 3x × (x + 4) = 3x² + 12x.

Multiplication of Polynomials

Polynomial by Polynomial: Multiply each term of one polynomial by each term of the other.

Example: (x + 2) × (x + 3) = x² + 3x + 2x + 6 = x² + 5x + 6.

Standard Identities in Algebra

Common Algebraic Identities

Identity 1: (a + b)² = a² + 2ab + b²

Example: If a = 2 and b = 3, then (2 + 3)² = 25.

Identity 2: (a − b)² = a² − 2ab + b²

Example: If a = 5 and b = 2, then (5 − 2)² = 9.

Identity 3: a² − b² = (a + b)(a − b)

Example: If a = 6 and b = 4, then 6² − 4² = 100.

Application of Algebraic Identities

Simplification: Use identities to simplify complex algebraic expressions.

Example: Simplify (x + 3)² − (x − 2)² using the identity a² − b² = (a + b)(a − b).

Scenario-Based Mathematics Problems

Scenario 1: Finance and Budgeting

Problem: Raj is budgeting his expenses for the month. He spends 2x on groceries, 3x on rent, and 5x on utilities. Express his total monthly expenses as an algebraic expression.

Solution: The total expenses can be expressed as 2x + 3x + 5x = 10x.

Scenario 2: Construction and Area Calculation

Problem: A rectangular garden has a length of l meters and a width of w meters. If the length is 2 meters more than the width, express the area of the garden as an algebraic expression.

Solution: Since l = w + 2, the area A is given by A = l × w = (w + 2) × w = w² + 2w.

Scenario 3: Profit Calculation

Problem: A shopkeeper buys x items at a cost of ₹20 each and sells them at ₹30 each. Write an expression for the profit made by the shopkeeper.

Solution: The profit for each item is ₹30 − ₹20 = ₹10, so the total profit is 10x.

Key Terms and Concepts

Terms

Definition: Parts of an algebraic expression separated by plus or minus signs.

Coefficient

Definition: The numerical factor in a term of an algebraic expression.

Identity

Definition: An equation that holds true for all values of its variables.

Polynomial

Definition: An algebraic expression with more than one term.

Chronology of Key Concepts

  1. Introduction to Algebraic Expressions: Understanding basic components like terms and coefficients.
  2. Addition and Subtraction: Learning to combine like terms.
  3. Multiplication: Expanding expressions using distributive property.
  4. Algebraic Identities: Applying identities to simplify expressions.
  5. Real-life Applications: Using algebra in practical scenarios.

Additional Value Addition

Real-life Applications of Algebraic Identities

Engineering: Algebraic identities are used in designing structures, electronics, and in solving complex equations in physics.

Example: Calculating the force on a bridge using algebraic identities.

Technology: Computer algorithms often rely on algebraic expressions to function efficiently.

Example: Optimizing search engines using polynomial equations.
FAQ: Algebraic Expressions and Identities

FAQ: Algebraic Expressions and Identities

1. What is an algebraic expression?

An algebraic expression is a mathematical phrase that can include numbers, variables, and operations. For example, 3x + 5 is an algebraic expression.

2. What are the terms in an algebraic expression?

Terms are the individual parts of an algebraic expression, separated by plus or minus signs. In 3x + 5, both 3x and 5 are terms.

3. What is a coefficient?

The coefficient is the numerical factor of a term in an algebraic expression. For example, in 3x, 3 is the coefficient.

4. What is a monomial?

A monomial is an algebraic expression that consists of only one term, such as 7xy.

5. How do you add algebraic expressions?

To add algebraic expressions, combine like terms, which are terms with the same variables raised to the same power. For example, 3x + 4x = 7x.

6. What is a binomial?

A binomial is an algebraic expression that consists of two terms, such as a + b.

7. What is a polynomial?

A polynomial is an algebraic expression with more than one term. For example, x² + 3x + 4 is a polynomial.

8. How do you multiply a monomial by a monomial?

To multiply a monomial by another monomial, multiply the coefficients and then the variables. For example, 3x × 4x = 12x².

9. What is an identity in algebra?

An identity in algebra is an equation that holds true for all values of its variables. For example, (a + b)² = a² + 2ab + b² is an identity.

10. What does it mean to combine like terms?

Combining like terms means adding or subtracting terms that have the same variable and exponent. For instance, 2x and 3x are like terms and can be combined to make 5x.

11. How do you multiply a polynomial by a monomial?

To multiply a polynomial by a monomial, distribute the monomial to each term in the polynomial. For example, 3x × (x + 4) = 3x² + 12x.

12. What is the difference between a term and a factor?

A term is a part of an algebraic expression, separated by plus or minus signs, while a factor is a quantity that is multiplied by another quantity. In 3x, 3x is a term and 3 and x are factors.

13. How do you apply the identity (a + b)² = a² + 2ab + b²?

To apply the identity (a + b)² = a² + 2ab + b², substitute the values of a and b into the formula. For example, if a = 2 and b = 3, (2 + 3)² = 4 + 12 + 9 = 25.

14. What is the product of (a + b)(a − b)?

The product of (a + b)(a − b) is given by the identity a² − b².

15. How do you multiply polynomials?

To multiply polynomials, multiply each term in the first polynomial by each term in the second polynomial and combine like terms. For example, (x + 2) × (x + 3) = x² + 3x + 2x + 6 = x² + 5x + 6.

16. What is a real-life application of algebraic expressions?

Algebraic expressions are used in finance for budgeting, construction for area calculations, and many other real-life scenarios where relationships between quantities need to be expressed mathematically.

17. How do you simplify an expression using the identity a² − b² = (a + b)(a − b)?

To simplify an expression using a² − b² = (a + b)(a − b), identify the expression in the form of a² − b² and apply the identity. For example, x² − 4 = (x + 2)(x − 2).

18. What are the components of a polynomial?

A polynomial consists of terms that may include coefficients, variables, and exponents. The degree of the polynomial is determined by the highest exponent.

19. How can you expand (x + y)²?

You can expand (x + y)² using the identity (a + b)² = a² + 2ab + b². For example, (x + y)² = x² + 2xy + y².

20. How do you subtract algebraic expressions?

To subtract algebraic expressions, distribute the negative sign to each term of the expression being subtracted and then combine like terms.

21. What is the importance of algebraic identities in simplification?

Algebraic identities are crucial for simplifying complex expressions and solving equations more efficiently by applying known formulas.

22. How do you find the value of an algebraic expression for a given value of the variable?

To find the value of an algebraic expression for a given value of the variable, substitute the variable with the given value and perform the arithmetic operations.

23. Can you give an example of using an algebraic expression in budgeting?

In budgeting, if x represents the amount spent on groceries and y represents the amount spent on utilities, the total monthly expense can be expressed as x + y.

24. What are like terms?

Like terms are terms in an algebraic expression that have the same variables raised to the same powers. They can be combined through addition or subtraction.

25. How do you apply the distributive property to simplify expressions?

The distributive property states that a(b + c) = ab + ac. To simplify an expression, distribute the multiplier across the terms inside the parentheses.

MCQs on Chapter 8: Algebraic Expressions and Identities

MCQs on Chapter 8: Algebraic Expressions and Identities

1. What is the coefficient of x in the expression 3x + 7?

2. Which of the following is a binomial?

3. What is the identity for (a + b)²?

4. What is the product of (x + 2) and (x + 3)?

5. Which of the following expressions is a monomial?

6. What is the sum of 3x and 5x?

7. What is the product of (a + b)(a – b)?

8. What is the coefficient in the term -7xy?

9. Expand the expression (x + 2)²

10. What is the simplified form of 2x + 3x – 4x?

11. Which expression is a polynomial?

12. What is the product of (x – 3)(x + 3)?

13. Which of the following identities represents the expansion of (a – b)²?

14. What is the expression for the square of (x + y)?

15. What is the value of the expression 2a + 3b when a = 2 and b = 3?

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