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3.3 - Algebraic Methods of Solving a Pair of Linear Equations

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Introduction to Algebraic Methods

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Teacher
Teacher

Today, we will discuss algebraic methods for solving pairs of linear equations. Why do you think algebraic methods might be needed if we already have a graphical method?

Student 1
Student 1

Maybe because we sometimes get non-integer answers that are hard to graph?

Student 2
Student 2

Yes! Also, it could be easier to just do algebra than trying to draw a graph.

Teacher
Teacher

Exactly! Graphical methods can be tricky with points like (3.5, 2.7). Let's dive into the first algebraic method: substitution.

Substitution Method

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Teacher
Teacher

Let's start with the substitution method. Who can tell me the first step when using this method?

Student 3
Student 3

We need to pick one equation and solve for one variable?

Teacher
Teacher

Correct! For example, if we have the equations 7x - 15y = 2 and x + 2y = 3, we can isolate x in the second equation. Can someone show how to solve for x?

Student 4
Student 4

Sure, x = 3 - 2y.

Teacher
Teacher

Great! Now we substitute that into the first equation. Can you do that?

Student 1
Student 1

So we replace x in the first equation, right?

Teacher
Teacher

Exactly! Let’s solve it together.

Elimination Method

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Teacher
Teacher

Now let's move on to the elimination method. Why might a student choose elimination over substitution?

Student 2
Student 2

Elimination might be easier for some equations, especially when the coefficients are already aligned.

Teacher
Teacher

Exactly! For instance, let's look at incomes given by 9x - 4y = 2000 and 7x - 3y = 2000. How do we make the y coefficients equal?

Student 3
Student 3

We could multiply the first equation by 3 and the second by 4.

Teacher
Teacher

Perfect! Now, we can eliminate y by subtracting the two equations. Let's solve for x.

Comparing Methods

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Teacher
Teacher

Let's compare both methods we've learned. When do you think you'd prefer one method over the other?

Student 4
Student 4

Maybe I would use substitution if one variable is already isolated in an equation.

Student 1
Student 1

And I'd choose elimination when the coefficients are easy to manipulate.

Teacher
Teacher

Great observations! Both methods are valid, and it's about finding which fits best for the given equations.

Recap of Key Concepts

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Teacher
Teacher

To wrap up, can anyone summarize the key steps of the substitution method?

Student 2
Student 2

First, isolate a variable in one equation, then substitute it into the other equation to solve for the second variable.

Student 3
Student 3

And for elimination, we adjust both equations to align the coefficients and eliminate one variable by adding or subtracting!

Teacher
Teacher

Fantastic! Remember, knowing when to use which method is crucial for efficiency in solving linear equations.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section explores algebraic methods for solving pairs of linear equations, focusing on substitution and elimination methods.

Standard

The section provides a comprehensive overview of two key algebraic methods for solving linear equations: the substitution method and the elimination method. Each method is explained through examples that demonstrate the steps involved, ensuring the reader understands how to apply them in various scenarios.

Detailed

Detailed Summary

This section of the chapter focuses on algebraic methods to solve pairs of linear equations. While the graphical method has its uses, it can be impractical when dealing with non-integer solutions. Therefore, we introduce two effective algebraic methods: substitution and elimination.

1. Substitution Method

The substitution method involves solving one equation for one variable and substituting that expression into the other equation. We illustrated this method with several examples, ensuring clarity through step-by-step analyses. Key steps include:

  • Choose one equation and isolate one variable.
  • Substitute this expression into the other equation.
  • Solve for the remaining variable and substitute back to find the original variable.

Example 4 demonstrates the substitution method for the equations 7x - 15y = 2 and x + 2y = 3.

2. Elimination Method

The elimination method focuses on eliminating one variable through addition or subtraction of equations. This is often more straightforward in cases where coefficients of a variable can be made equal. In this method, one multiplies equations as necessary, then subtracts or adds to eliminate a variable. Example 8 illustrates this method through a real-world situation involving incomes and expenditures.

Summary of Concepts

  • The graphical method can be impractical for non-integral solutions.
  • Substitution is useful for isolating variables, while elimination simplifies the process of removal.
  • Both methods can be applied to numerous scenarios involving linear equations.

By mastering these algebraic methods, students can confidently solve pairs of linear equations and apply these techniques to complex problems in mathematics.

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Audio Book

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Introduction to Algebraic Methods

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In the previous section, we discussed how to solve a pair of linear equations graphically. The graphical method is not convenient in cases when the point representing the
solution of the linear equations has non-integral coordinates like (3, 2.7), (–1.75, 3.3), etc. There is every possibility of making mistakes while reading such coordinates. Is there any alternative method of finding the solution? There are several algebraic methods, which we shall now discuss.

Detailed Explanation

The introduction highlights the limitations of using graphical methods for solving linear equations, particularly when solutions yield non-integer coordinates. Instead, it sets the stage for exploring algebraic methods, which are more precise and eliminate the possibility of errors in reading graphs. These methods can be employed to solve equations with exact numerical answers, avoiding confusion with coordinates that are difficult to interpret.

Examples & Analogies

Imagine trying to hit a precise target with a dart from a distance. If you blindfold yourself, you're guessing where the dart lands, which is like using a graph - sometimes you miss the exact point. Now, if you use a ruler and measure directly from a table, it's like using algebra - every calculation is precise, and you can be confident about your aim.

Substitution Method: Steps and Examples

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3.3.1 Substitution Method : We shall explain the method of substitution by taking some examples. Example 4: Solve the following pair of equations by substitution method: 7x – 15y = 2 (1) x + 2y = 3 (2) Solution: Step 1: We pick either of the equations and write one variable in terms of the other...

Detailed Explanation

The substitution method involves three steps. First, choose an equation and rearrange it to express one variable in terms of the other. Next, substitute this expression into the other equation to solve for the remaining variable. Finally, once that variable is determined, substitute it back to find the value of the first one. This method is advantageous because it is often simpler and clearer than others, especially when one equation can easily be solved for one variable.

Examples & Analogies

Think of a recipe where you need to find how many cups of flour (x) and sugar (y) you need. If the recipe says to use 2 cups of sugar for every cup of flour, you can write the sugar in terms of flour and solve how much flour you actually need. This is similar to how substitution simplifies equations.

Working with Real-World Problems

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Example 5: Solve the age problem: Aftab tells his daughter, “Seven years ago, I was seven times as old as you were then. Also, three years from now, I shall be three times as old as you will be.” ...

Detailed Explanation

In this example, two relationships regarding the ages of Aftab and his daughter are created as linear equations. We formulate these equations based on the conditions given and then apply the substitution method to find the ages of both. The structured breakdown of the problem into equations illustrates the power of algebra in solving real-life situations, providing clarity and a straightforward approach to the problem.

Examples & Analogies

Consider how detectives form a case based on clues. Just like detectives set up connections and relationships between suspects and evidence, you are establishing relationships between ages to find the solution. Each equation is a clue that leads to unraveling the mystery of their ages.

Exploring Limitations and Variability in Systems

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Example 6: In a shop, the cost of 2 pencils and 3 erasers is 9 and the cost of 4 pencils and 6 erasers is18...

Detailed Explanation

In this situation, while forming equations based on given data, we find both equations represent the same line when solved. This leads to the conclusion that there are infinitely many solutions because the two prices essentially express the same relationship and do not provide unique prices for pencils and erasers. This serves as a practical illustration of when two equations might coincide and highlights the concept of dependent equations in algebra.

Examples & Analogies

Imagine filling a cup with water—it can be filled in many ways (sipping slowly or pouring fast) but always ends up at the same level. Here, the two price equations end up describing the same relationship - how the quantities of pencils and erasers relate to the total cost—implying multiple paths can lead to the same relationship.

The Elimination Method

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3.3.2 Elimination Method: Now let us consider another method of eliminating (i.e., removing) one variable. This is sometimes more convenient than the substitution method...

Detailed Explanation

The elimination method includes first aligning coefficients for one of the variables by multiplying the equations, then either adding or subtracting the equations to eliminate that variable. The resulting equation can be solved for the other variable, with steps to verify the solution afterward. This method works effectively in scenarios where substitution becomes cumbersome, demonstrating its flexibility and reliability in solving linear equations.

Examples & Analogies

Think of two teams competing in a relay race where you need to figure out how much lead one team has over the other. By adjusting how much each team's positions are adjusted relative to the start with each lap, you can figure out who is ahead without having to track every runner individually—this is akin to how elimination allows you to simplify solving equations.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Algebraic Methods: Algebraic methods like substitution and elimination are used to solve pairs of linear equations analytically.

  • Substitution Method: A method where one variable is expressed in terms of another, allowing for direct substitution into an equation.

  • Elimination Method: A technique that involves modifying equations to eliminate one variable, facilitating easier solutions.

  • Consistent vs. Inconsistent: Determines the existence of solutions based on the relationship between the equations.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Example 4: Using substitution, solve the equations 7x - 15y = 2 and x + 2y = 3.

  • Example 8: Using elimination, determine monthly incomes from the equations based on savings.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • When you're stuck and need a clue, substitute the known, it's what you do.

📖 Fascinating Stories

  • Imagine two friends trying to find out how many candies they each have. One tells the other their total and how much they owe. By substituting and eliminating what's known, they figure out that together they have 16 candies!

🧠 Other Memory Gems

  • S.E.S (Substitution, Equation, Solve) – using substitution, set the equation, then solve!

🎯 Super Acronyms

C.E.S (Coefficients, Eliminate, Solve) – identify coefficients, eliminate one variable, and solve!

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Substitution Method

    Definition:

    An approach to solving linear equations where one variable is expressed in terms of the other and substituted back into the equations.

  • Term: Elimination Method

    Definition:

    A way of solving systems of equations by removing one variable through addition or subtraction of the equations.

  • Term: Linear Equations

    Definition:

    Equations that form a straight line when graphed, typically represented in the form ax + by + c = 0.

  • Term: Coefficient

    Definition:

    A numerical factor in a term of an algebraic expression.

  • Term: Inconsistent

    Definition:

    Describes a system of equations that has no solution.

  • Term: Consistent

    Definition:

    Describes a system of equations that has at least one solution.

  • Term: Dependent Equations

    Definition:

    Equations that represent the same line and thus have infinitely many solutions.