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Introduction to Algebraic Expressions

Algebraic expressions form the backbone of algebra, combining numbers, variables, and mathematical operations (addition, subtraction, multiplication, division, and exponentiation) to represent relationships and solve problems. A variable, typically denoted by letters like x, y, or z, represents an unknown or changeable value, while a constant is a fixed numerical value. Understanding algebraic expressions is crucial for modeling real-world scenarios, such as calculating costs, distances, or areas, and is foundational for advanced mathematical concepts.

Expressions are classified by the number of terms they contain: monomials (1 term), binomials (2 terms), trinomials (3 terms), or polynomials (multiple terms). Terms are separated by addition or subtraction and consist of coefficients, variables, and exponents.

Tip: Always identify the type of expression (monomial, binomial, etc.) before performing operations, as it helps in organizing your approach to simplification or factorization.

Key Concepts

1. Constants, Variables, and Terms

A constant is a number with a fixed value (e.g., 5, -3, π). A variable is a symbol that can take any value from a given set, often represented by letters like x, y, or z. A term is a single number, variable, or a product/quotient of numbers and variables (e.g., 4x², -7, xy). Terms are combined using operations to form expressions.

Example 1: Identify constants and variables in 8x + 5y - 3.
Ans: Constants = -3; Variables = x, y.

Example 2: Classify 2x² + 3x - 7.
Ans: This is a trinomial with three terms: 2x², 3x, -7.

2. Coefficients

The coefficient of a term is the factor (numerical or variable) multiplying the variable part. For example, in -5xy, the coefficient of xy is -5. If a term has multiple variables, the coefficient depends on which variable is being considered.

Example 1: Find the coefficient of xy in -3axy.
Ans: The coefficient of xy is -3a.

Example 2: Find the coefficient of z² in p²yz².
Ans: The coefficient of z² is p²y.

Warning: Be careful to include all parts of the coefficient, including any variable factors, when identifying coefficients of specific variable terms.

3. Degree of a Polynomial

The degree of a polynomial is the highest sum of the exponents of the variables in any single term. For monomials, it’s the sum of the exponents of all variables. For polynomials, it’s the highest degree among all terms. The degree helps determine the behavior of the polynomial, such as its graph’s shape.

Example 1: Find the degree of -2x²y.
Ans:Degree = 2 (x²) + 1 (y) = 3.

Example 2: Find the degree of 3x²z + 5yz³.
Ans: Degree of 3x²z = 2 + 1 = 3; degree of 5yz³ = 1 + 3 = 4. The highest degree is 4.

4. Like and Unlike Terms

Like terms have identical variable parts with the same exponents (e.g., 4x² and -2x²). Unlike terms differ in their variable parts or exponents (e.g., xy and x²y). Only like terms can be combined by adding or subtracting their coefficients.

Example 1: Group the like terms: 7x², xy, -3x², x², -5xy.
Ans: Like terms: 7x², -3x², x²; xy, -5xy.

Example 2: Group the like terms: ab, -2ab, -a²b, 4a²b, -6a²b.
Ans:Like terms: ab, -2ab; -a²b, 4a²b, -6a²b.

Tip: When grouping like terms, check both the variables and their exponents carefully to avoid errors.

5. Addition and Subtraction of Algebraic Expressions

Add or subtract algebraic expressions by combining like terms. Align terms with the same variable parts and add or subtract their coefficients. When subtracting, distribute the negative sign across all terms in the subtracted expression.

Example 1: Simplify 8x + 4x + 5x.
Ans: 8x + 4x + 5x = (8 + 4 + 5)x = 17x.

Example 2: Subtract 3a + 2b from 5a + 7b.
Ans: (5a + 7b) - (3a + 2b) = 5a + 7b - 3a - 2b = 2a + 5b.

Example 3: Simplify 9x² - 6x + 7 + 5 - 4x + 6 - 3x².
Ans:  9x² - 6x + 7 + 5 - 4x + 6 - 3x²
 = (9x² - 3x²) + (-6x - 4x) + (7 + 5 + 6)
 = 6x² - 10x + 18 

6. Multiplication of Algebraic Expressions

Monomials: Multiply coefficients and add the exponents of like variables.
Polynomials: Use the distributive property to multiply each term of one polynomial by each term of the other, then combine like terms. Special identities, like (a + b)(a - b) = a² - b², can simplify calculations.

Note: When multiplying polynomials, ensure all terms are multiplied systematically to avoid missing any terms.

Example 1: Multiply 2x, 4x²y, and 3y.
Ans: 2x × 4x²y × 3y = 2 × 4 × 3 × x¹⁺² × y¹⁺¹ = 24x³y².

Example 2: Multiply (3x + 2y)(3x - 2y).
Ans:  (3x + 2y)(3x - 2y) = (3x)² - (2y)²
 = 9x² - 4y² 

Example 3: Multiply (2x + 3y)(x - y).
Ans:  2x(x - y) + 3y(x - y)
 = 2x² - 2xy + 3xy - 3y²
 = 2x² + xy - 3y² 

7. Division of Algebraic Expressions

Monomial by Monomial: Divide coefficients and subtract exponents of like variables.
Polynomial by Monomial: Divide each term of the polynomial by the monomial and simplify.
Polynomial by Polynomial: Use polynomial long division, arranging terms in descending or ascending order of exponents.

Example 1: Divide 16x³y² - 12x²y³ by 4xy.
Ans:  (16x³y² - 12x²y³) ÷ 4xy
 = (16x³y² ÷ 4xy) - (12x²y³ ÷ 4xy)
 = 4x²y - 3xy² 

Example 2: Divide x² + 6x + 9 by x + 3.
Ans:  x + 3 ) x² + 6x + 9 ( x + 3
           x² + 3x
           ----------
              3x + 9
              3x + 9
              ----------
              0
 Quotient = x + 3 

Warning: When dividing by a monomial, ensure the variable exponents in the numerator are greater than or equal to those in the denominator to avoid negative exponents.

8. Simplifying Algebraic Fractions

Algebraic fractions involve variables in the numerator, denominator, or both. To simplify, find a common denominator, combine terms, and simplify the resulting expression. When dealing with complex fractions, simplify the inner expressions first.

Example 1: Simplify (3x/4) + (x/6).
Ans: (3x/4) + (x/6)
 = (3x×3 + x×2)/12
 = (9x + 2x)/12
 = 11x/12 

Example 2: Simplify (2a/3) - (a/5) + (a/2).
Ans:  (2a/3) - (a/5) + (a/2)
 = (2a×10 - a×6 + a×15)/30
 = (20a - 6a + 15a)/30
 = 29a/30 

Example 3: Simplify (x/5) + (x+2)/3.
Ans:  (x/5) + (x+2)/3
 = (x×3 + (x+2)×5)/15
 = (3x + 5x + 10)/15
 = (8x + 10)/15
 = (8x + 10) ÷ 5 / 15 ÷ 5
 = (8x + 10)/15 

Applications of Algebraic Expressions

Algebraic expressions are widely used in solving real-world problems, such as calculating perimeters, areas, or volumes of geometric shapes, modeling financial scenarios, or analyzing physical quantities like speed and distance.

Example 1: The sides of a triangle are 3x + 4y, 2x + 6y, and 5x - y. Find its perimeter.
Ans:  Perimeter = (3x + 4y) + (2x + 6y) + (5x - y)
 = (3x + 2x + 5x) + (4y + 6y - y)
 = 10x + 9y 

Example 2: The area of a rectangle is 25x² + 20xy + 3y², and its length is 5x + 3y. Find its breadth and perimeter.
Ans:  Breadth = Area ÷ Length
 = (25x² + 20xy + 3y²) ÷ (5x + 3y)
 5x + 3y ) 25x² + 20xy + 3y² ( 5x + y
              25x² + 15xy
              ------------
                  5xy + 3y²
                  5xy + 3y²
                  ------------
                  0
 Breadth = 5x + y
 Perimeter = 2(Length + Breadth) = 2((5x + 3y) + (5x + y)) = 2(10x + 4y) = 20x + 8y 

Example 3: What must be subtracted from a² + b² + 2ab to get -4ab + 2b²?
Ans:  Let the expression to be subtracted be X.
 a² + b² + 2ab - X = -4ab + 2b²
 X = a² + b² + 2ab - (-4ab + 2b²)
 = a² + b² + 2ab + 4ab - 2b²
 = a² - b² + 6ab 

Advanced Simplification Techniques

Complex expressions often involve nested brackets or multiple operations. Simplify by expanding brackets, combining like terms, and applying identities where applicable.

Example 1: Simplify 5x - [3y - (2x + y) + x].
Ans:  5x - [3y - (2x + y) + x]
 = 5x - [3y - 2x - y + x]
 = 5x - [3y - y - 2x + x]
 = 5x - [2y - x]
 = 5x - 2y + x
 = 6x - 2y 

Example 2: Simplify 2[a - 3(a + 5(a - 2) + 7)].
Solution:  2[a - 3(a + 5(a - 2) + 7)]
 = 2[a - 3(a + 5a - 10 + 7)]
 = 2[a - 3(6a - 3)]
 = 2[a - 18a + 9]
 = 2[-17a + 9]
 = -34a + 18 

Tip: When dealing with nested brackets, simplify the innermost brackets first and work outward to avoid errors.

The document Fundamental Concepts Chapter Notes | Mathematics Class 7 ICSE is a part of the Class 7 Course Mathematics Class 7 ICSE.
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FAQs on Fundamental Concepts Chapter Notes - Mathematics Class 7 ICSE

1. What is an algebraic expression and how is it different from a numerical expression?
Ans. An algebraic expression is a combination of numbers, variables, and arithmetic operations (such as addition, subtraction, multiplication, and division). For example, 3x + 5 is an algebraic expression, where 'x' is a variable. In contrast, a numerical expression consists only of numbers and operations, such as 4 + 6 or 12 × 3, without any variables. The key difference is that algebraic expressions can represent a range of values depending on the variable, whereas numerical expressions have a fixed value.
2. How can algebraic expressions be simplified?
Ans. Algebraic expressions can be simplified by combining like terms, which are terms that contain the same variable raised to the same power. For example, in the expression 2x + 3x, both terms contain the variable 'x', so they can be combined to form 5x. Additionally, applying the distributive property, such as a(b + c) = ab + ac, can help in simplifying expressions further. Always ensure to follow the order of operations when simplifying.
3. What are the applications of algebraic expressions in real life?
Ans. Algebraic expressions have various applications in real life, including in fields such as finance, engineering, and science. For instance, they are used to calculate profits and losses in business (e.g., revenue = price × quantity sold), to model physical phenomena in physics (e.g., distance = speed × time), and in statistics for representing data trends. Algebraic expressions help in solving problems by providing a systematic way to represent relationships between quantities.
4. What are some advanced techniques for simplifying algebraic expressions?
Ans. Advanced techniques for simplifying algebraic expressions include factoring, using the quadratic formula, and employing identities like the difference of squares or perfect square trinomials. For example, the expression x² - 9 can be factored into (x - 3)(x + 3) using the difference of squares identity. Additionally, recognizing patterns and using substitution can lead to more efficient simplifications.
5. How can one identify like and unlike terms in algebraic expressions?
Ans. Like terms are those that have the same variable part raised to the same power. For example, in the expression 3x² + 5x² + 2xy, the terms 3x² and 5x² are like terms because they both contain x². Unlike terms have different variable parts or powers; for instance, 2xy and 3x² are unlike terms. To identify like terms, look at the variables and their exponents, ensuring they match exactly.
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