Chapter 5: Introduction to Algebra
[First Half: Foundations of Algebra]
5.1: Introduction to Algebra
Algebra is a branch of mathematics that extends the concepts of arithmetic by introducing variables, which are symbols that represent unknown or changing quantities. This transition from arithmetic to algebra marks a significant step in mathematical reasoning and problemsolving.
In arithmetic, we work with known numbers and perform operations such as addition, subtraction, multiplication, and division to find specific values. However, in algebra, we use variables to represent unknown or changing values, allowing us to explore and solve more general and abstract problems.
The primary advantages of using algebra are:

Generalization: Algebra allows us to represent and solve problems in a more general way, without being limited to specific numerical values. This enables us to discover and apply patterns, formulas, and relationships that hold true for a wider range of situations.

Unknowns and Variables: Algebra introduces the concept of variables, which are symbols (such as x, y, or z) that represent unknown or changing quantities. This allows us to solve for the unknown values in equations and expressions.

Modeling RealWorld Situations: Algebraic techniques can be used to create mathematical models that represent realworld problems, enabling us to analyze, predict, and find solutions to complex scenarios.
By understanding the fundamental differences between arithmetic and algebra, students will be better equipped to transition into the world of algebraic thinking and problemsolving.
Key Takeaways:
 Algebra extends arithmetic by introducing variables to represent unknown or changing quantities.
 Algebra allows for the generalization of problems, enabling the discovery of patterns and relationships.
 The use of variables in algebraic expressions and equations is a core concept that distinguishes algebra from arithmetic.
 Algebraic modeling allows us to represent and solve realworld problems in a more abstract and powerful way.
5.2: Variables and Algebraic Expressions
In algebra, variables are used to represent unknown or changing quantities. These variables are typically represented by letters, such as x, y, or z. The main properties of variables are:
 Representing Unknown Values: Variables can be used to stand for numbers or quantities that are not yet known or specified.
 Representing Changing Values: Variables can represent values that may change or vary within a problem or situation.
 Holding the Place of a Number: Variables act as placeholders, allowing us to work with expressions and equations without knowing the exact numerical values.
Algebraic expressions are mathematical statements that involve variables, numbers, and operations (addition, subtraction, multiplication, and division). These expressions can take various forms, such as:
 Monomials: Expressions with a single term, such as 3x or 5y².
 Binomials: Expressions with two terms, such as 2x + 4 or y²  3y.
 Polynomials: Expressions with multiple terms, such as 2x² + 3x  5 or 4z³  2z + 7.
When working with algebraic expressions, it is essential to understand the rules for combining like terms, which are terms that have the same variables and exponents. The key rules are:
 Combining Like Terms: To combine like terms, we add or subtract the coefficients (the numbers in front of the variables) while keeping the variables the same. Example: 3x + 2x = 5x
 Performing Operations: We can perform the four basic operations (addition, subtraction, multiplication, and division) on algebraic expressions, following the order of operations (PEMDAS: Parentheses, Exponents, Multiplication and Division, Addition and Subtraction). Example: (2x + 3)  (x  1) = 2x + 3  x + 1 = x + 4
Mastering the understanding of variables and the manipulation of algebraic expressions is essential for success in solving more complex algebraic problems and equations.
Key Takeaways:
 Variables are used to represent unknown or changing quantities in algebra.
 Algebraic expressions are mathematical statements that involve variables, numbers, and operations.
 There are rules for combining like terms and performing operations on algebraic expressions.
 Understanding variables and the structure of algebraic expressions is fundamental to working with algebra.
5.3: Evaluating Algebraic Expressions
Evaluating algebraic expressions involves finding the numerical value of an expression when specific values are assigned to the variables. This skill is crucial for solving realworld problems and understanding the behavior of mathematical relationships.
The process of evaluating an algebraic expression follows these steps:
 Identify the Variables: Determine the variables present in the expression and their respective symbols (e.g., x, y, z).
 Substitute the Given Values: Replace each variable in the expression with the given numerical value.
 Simplify the Expression: Perform the necessary operations (addition, subtraction, multiplication, and division) following the order of operations (PEMDAS) to compute the final numerical value.
For example, consider the expression 2x²  3x + 4, where we want to evaluate it for x = 5.
 The variables in the expression are x.
 Substitute x = 5 into the expression: 2x²  3x + 4 = 2(5)²  3(5) + 4 = 2(25)  15 + 4
 Simplify the expression: = 50  15 + 4 = 39
By evaluating the expression with the given value of x, we can determine the numerical result, which in this case is 39.
Evaluating algebraic expressions is essential for solving equations, understanding the behavior of functions, and applying algebra to realworld situations. It allows us to explore the relationships between variables and their corresponding values, which is a crucial skill in the development of mathematical problemsolving abilities.
Key Takeaways:
 Evaluating an algebraic expression involves substituting specific values for the variables and then simplifying the expression.
 The process involves identifying the variables, substituting the given values, and performing the necessary operations.
 Evaluating expressions is a fundamental skill in algebra, as it allows us to understand the relationships between variables and their corresponding values.
5.4: Solving Simple Equations
An equation is a mathematical statement that expresses the equality between two algebraic expressions. Solving an equation means finding the value(s) of the variable(s) that make the equation true.
The basic principles of solving simple linear equations with one variable are as follows:
 Isolate the Variable: The goal is to isolate the variable on one side of the equation by performing inverse operations (addition, subtraction, multiplication, or division) on both sides of the equation.
 Apply the Properties of Equality: The properties of equality state that whatever you do to one side of the equation, you must do the same to the other side to maintain the balance.
 Find the Solution: Once the variable is isolated, you can determine the value of the variable that satisfies the equation.
Let's consider an example: Solve the equation 2x + 5 = 17.

Isolate the variable: 2x + 5 = 17 2x = 17  5 2x = 12 x = 12 / 2 x = 6

Check the solution: Substitute x = 6 back into the original equation: 2(6) + 5 = 17 12 + 5 = 17 17 = 17 (the equation is true)
Therefore, the solution to the equation 2x + 5 = 17 is x = 6.
Solving simple linear equations is a fundamental skill in algebra that lays the groundwork for solving more complex equations and systems of equations. It enables students to find unknown values, understand the relationships between variables, and apply algebraic techniques to realworld problemsolving.
Key Takeaways:
 Solving an equation means finding the value(s) of the variable(s) that make the equation true.
 The key steps are to isolate the variable by applying inverse operations and then use the properties of equality to find the solution.
 Solving simple linear equations is a crucial skill that prepares students for more advanced algebraic problemsolving.
[Second Half: Solving Problems with Algebra]
5.5: Modeling RealWorld Situations with Equations
Algebra provides a powerful tool for modeling realworld situations and solving practical problems. By translating word problems into algebraic equations, we can apply our understanding of variables, expressions, and equations to find solutions to complex scenarios.
The process of modeling realworld situations with equations involves the following steps:
 Understand the Problem: Carefully read and comprehend the given problem, identifying the key information, the unknown quantities, and the relationships between them.
 Define the Variables: Assign appropriate variables to represent the unknown or changing quantities in the problem.
 Translate the Relationships: Express the relationships and conditions described in the problem using algebraic expressions and equations.
 Solve the Equation: Apply the techniques of solving equations to find the value(s) of the variable(s) that satisfy the equation and, consequently, the original problem.
 Interpret the Solution: Analyze the solution in the context of the original problem and provide a meaningful interpretation of the result.
Consider the following example:
"A bakery sells muffins and cookies. Each muffin costs $2, and each cookie costs$1. If the bakery made a total of $200 in sales, and the number of muffins sold was twice the number of cookies sold, how many muffins and cookies were sold?"

Understand the problem:
 The bakery sells muffins and cookies.
 Muffins cost $2 each, and cookies cost$1 each.
 Total sales were $200.
 The number of muffins sold was twice the number of cookies sold.

Define the variables: Let x = the number of cookies sold Then, the number of muffins sold = 2x

Translate the relationships: Total revenue = (price of muffin × number of muffins) + (price of cookie × number of cookies) 200 = (2 × 2x) + (1 × x) 200 = 4x + x 200 = 5x

Solve the equation: 200 = 5x x = 200 / 5 x = 40

Interpret the solution: The number of cookies sold is 40. The number of muffins sold is 2 × 40 = 80.
By modeling the realworld situation as an algebraic equation, we were able to find the number of muffins and cookies sold, which satisfies the given conditions and information.
Key Takeaways:
 Algebraic modeling involves translating word problems into equations using variables and expressions.
 The process includes understanding the problem, defining the variables, translating the relationships, solving the equation, and interpreting the solution.
 Modeling realworld situations with equations is a powerful technique that allows us to apply algebraic problemsolving skills to practical problems.
5.6: Inequalities and Their Solutions
In algebra, an inequality is a mathematical statement that compares two expressions using symbols such as less than (<), greater than (>), less than or equal to (≤), or greater than or equal to (≥). Solving inequalities involves finding the set of values that satisfy the given inequality.
The basic principles of solving simple linear inequalities with one variable are as follows:
 Isolate the Variable: Perform inverse operations (addition, subtraction, multiplication, or division) on both sides of the inequality to isolate the variable.
 Maintain the Inequality Sign: When performing operations, the inequality sign must be reversed if the operation involves multiplying or dividing by a negative number.
 Identify the Solution Set: Determine the set of values for the variable that satisfy the inequality. This solution set can be represented using interval notation or by graphing the solution on a number line.
Let's consider an example: Solve the inequality 3x  5 ≥ 14.

Isolate the variable: 3x  5 ≥ 14 3x ≥ 14 + 5 3x ≥ 19 x ≥ 19 / 3 x ≥ 6.33 (rounded to two decimal places)

The inequality sign does not need to be reversed, as we are not multiplying or dividing by a negative number.

The solution set can be represented as: x ≥ 6.33
Or, it can be graphed on a number line as follows:

5 0 5 10 15 20 25
x ≥ 6.33
Solving inequalities is essential for understanding and representing the range of possible solutions to a problem. It allows us to analyze situations where there are constraints or limits on the values of variables, which is particularly useful in various realworld applications, such as in finance, economics, and decisionmaking.
Key Takeaways:
 Inequalities compare two expressions using symbols like less than, greater than, or equal to.
 Solving inequalities involves isolating the variable and maintaining the correct inequality sign.
 The solution set can be represented using interval notation or by graphing the solution on a number line.
 Solving inequalities is a valuable skill for understanding and representing the range of possible solutions in realworld problems.
5.7: Proportions and Rates of Change
Proportions and rates of change are important concepts in algebra that are widely applicable in various fields, from science and engineering to business and everyday life.
A proportion is a statement of equality between two ratios. Proportions can be used to solve problems involving scale factors, unit rates, and other situations where quantities are related by a constant ratio.
The key steps in solving proportions are:
 Identify the Quantities: Determine the quantities involved in the problem and how they are related.
 Set Up the Proportion: Write an equation that expresses the equality of the two ratios.
 CrossMultiply and Solve: Use the crossmultiplication property to solve for the unknown value in the proportion.
For example, consider the following problem: "If 3 pencils cost $1.50, how much would 7 pencils cost?"
 The quantities involved are the number of pencils and the cost.
 Set up the proportion: 3 pencils / $1.50 = 7 pencils / x
 Crossmultiply and solve for x: 3x = 7 × 1.50 x = 7 × 1.50 / 3 x = $3.50
Rates of change are a way of expressing how a quantity changes in relation to another quantity. In algebra, we often deal with linear relationships, where the rate of change is constant and can be represented by the slope of a line.
The slope of a line can be calculated using the formula: Slope = (y₂  y₁) / (x₂  x₁)
This slope formula allows us to determine the rate of change between two points on a line, which can be applied to solve problems involving unit rates, proportional relationships, and other realworld applications.
Key Takeaways:
 Proportions are statements of equality between two ratios, and they can be used to solve problems involving scale factors and unit rates.
 Solving proportions involves setting up the proportion and using the crossmultiplication property to find the unknown value.
 Rates of change, represented by the slope of a line, describe how one quantity changes in relation to another.
 Understanding proportions and rates of change is essential for solving a variety of realworld problems that involve linear relationships.
5.8: Chapter Review and Consolidation
In this final section, we will review the key concepts and skills covered in this chapter on the Introduction to Algebra.
Foundations of Algebra
 Understand the transition from arithmetic to algebra and the role of variables in algebraic thinking.
 Learn to work with variables and construct algebraic expressions, applying the rules for combining like terms and performing operations.
 Develop the ability to evaluate algebraic expressions by substituting specific values for the variables.
 Gain proficiency in solving simple linear equations by isolating the variable and applying the properties of equality.
Solving Problems with Algebra
 Explore the process of modeling realworld situations by translating word problems into algebraic equations and solving them.
 Understand the concept of inequalities, learn how to solve them, and represent the solution sets.
 Recognize and apply proportions to solve problems involving scale factors, unit rates, and other relationships.
 Understand the concept of rates of change and how to use the slope formula to analyze linear relationships.
Throughout the chapter, we have emphasized the importance of developing a solid foundation in algebraic concepts and then applying these skills to solve practical problems. By mastering the content in this chapter, students will be wellequipped to progress to more advanced algebraic topics and techniques.
To consolidate the learning, consider the following activities:
 Practice solving a variety of algebraic expressions and equations, including those with multiple steps and variables.
 Engage in word problemsolving exercises, translating the given information into algebraic models and finding solutions.
 Explore realworld applications of proportions and rates of change, such as scale