# 3.5 Use a General Strategy to Solve Linear Equations

Learning Objectives

By the end of this section, you will be able to:

• Solve equations using a general strategy
• Classify equations

# Solve Equations Using the General Strategy

Until now we have dealt with solving one specific form of a linear equation. It is time now to lay out one overall strategy that can be used to solve any linear equation. Some equations we solve will not require all these steps to solve, but many will.

Beginning by simplifying each side of the equation makes the remaining steps easier.

EXAMPLE 1. How to Solve Linear Equations Using the General Strategy

Solve: .
Solution
 Step 1. Simplify each side of the equation as much as possible. Use the Distributive Property. Notice that each side of the equation is simplified as much as possible. Step 2. Collect all variable terms on one side of the equation. Nothing to do as all the x’s are on the left side. Step 3. Collect constant terms on the other side of the equation. To get constants only on the right side, add 18 to each side. Simplify. Step 4. Make the coefficient of the variable term to equal to 1. Divide each side by . Simplify Step 5. Check the solution. Let

TRY IT 1.1

Solve: .

TRY IT 1.2

Solve: .

General strategy for solving linear equations.

1. Simplify each side of the equation as much as possible.
Use the Distributive Property to remove any parentheses.
Combine like terms.
2. Collect all the variable terms on one side of the equation.
Use the Addition or Subtraction Property of Equality.
3. Collect all the constant terms on the other side of the equation.
Use the Addition or Subtraction Property of Equality.
4. Make the coefficient of the variable term to equal to 1.
Use the Multiplication or Division Property of Equality.
State the solution to the equation.
5. Check the solution. Substitute the solution into the original equation to make sure the result is a true statement.

EXAMPLE 2

Solve: .

Solution

Given equation.

Simplify each side of the equation by distributing.

The only term is on the left side, so all variable terms are on the left side of the equation.

Add to both sides to get all constant terms on the right side of the equation.

Simplify.

Rewrite as .

Make the coefficient of the variable term to equal to by dividing both sides by .

Simplify.

Check:
Let .

TRY IT 2.1

Solve: .

TRY IT 2.2

Solve: .

EXAMPLE 3

Solve: .

Solution

Simplify each side of the equation as much as possible.

Distribute.

Combine like terms.

The only term containing is on the left side, so all variable terms are on one side of the equation.

Add 10 to both sides to get all constant terms on the other side of the equation.

Simplify.

Make the coefficient of the variable term to equal to 1 by dividing both sides by 5.

Simplify.

Check: Let

TRY IT 3.1

Solve: .

TRY IT 3.2

Solve: .

EXAMPLE 4

Solve: .

Solution

Distribute.

Simplify each side of the equation.

Add to get all the variables on the left side and simplify.

Add to get constants only on the right and simplify.

Make the coefficient of the variable term to equal to 1 by dividing both sides by 5.

Simplify.

Check: Let

TRY IT 4.1

Solve: .

TRY IT 4.2

Solve: .

EXAMPLE 5

Solve: .

Solution
Distribute
Simplify each side of the equation.

Combine like terms.

Add to get all the variables on the left side and simplify.

Make the coefficient of the variable term to equal to 1 by dividing both sides by .

Simplify.

Check: Let

TRY IT 5.1

Solve: .

TRY IT 5.2

Solve: .

EXAMPLE 6

Solve: .

Solution

Given equation.

Distribute.

Combine like terms.

Subtract 4x to get the variables only on the right side since 10 > 4.

Simplify.

Subtract 21 to get the constants on left and simplify.

Divide by 6 and simplify.

Check. Let

TRY IT 6.1

Solve: .

TRY IT 6.2

Solve: .

EXAMPLE 7

Solve: .

Solution

Given equation.

Distribute and simplify.

Distribute and combine like terms.

Add  to get the s’s to the right.

Simplify.

Subtract 600 to get the constants on left and simplify.

Divide by and simplify.

Check: Substitute

TRY IT 7.1

Solve: .

TRY IT 7.2

Solve: .

EXAMPLE 8

Solve: .

Solution

Given equation.

Distribute and simplify.

Subtract to get the n’s to the left.

Simplify.

Subtract 1.8 to get the constants on right and simplify.

Divide by and simplify.

Check: Substitute

TRY IT 8.1

Solve: .

TRY IT 8.2

Solve: .

# Classify Equations

Consider the equation we solved at the start of the last section, . The solution we found was . This means the equation is true when we replace the variable, x, with the value . We showed this when we checked the solution and evaluated for .

If we evaluate for a different value of x, the left side will not be .

The equation is true when we replace the variable, x, with the value , but not true when we replace x with any other value. Whether or not the equation is true depends on the value of the variable. Equations like this are called conditional equations.

All the equations we have solved so far are conditional equations.

Conditional equation

An equation that is true for one or more values of the variable and false for all other values of the variable is a conditional equation.

Now let’s consider the equation . Do you recognize that the left side and the right side are equivalent? Let’s see what happens when we solve for y.

 Distribute. Subtract to get the ’s to one side. Simplify—the ’s are gone!

But is true.

This means that the equation is true for any value of y. We say the solution to the equation is all of the real numbers. An equation that is true for any value of the variable like this is called an identity.

Identity

An equation that is true for any value of the variable is called an identity.

The solution of an identity is every real number.

What happens when we solve the equation ?

 Subtract to get the constant alone on the right. Simplify—the ’s are gone!

But .

Solving the equation led to the false statement . The equation will not be true for any value of z. It has no solution. An equation that has no solution, or that is false for all values of the variable, is called a contradiction.

An equation that is false for all values of the variable is called a contradiction.

EXAMPLE 9

Classify the equation as a conditional equation, an identity, or a contradiction. Then state the solution.

Solution

Given equation.

Distribute and combine like terms.

Subtract from both sides to get the ’s to one side and simplify.

This equation is a true statement.

The equation is an identity.
The solution is every real number.

TRY IT 9.1

Classify the equation as a conditional equation, an identity, or a contradiction and then state the solution:

identity; all real numbers

TRY IT 9.2

Classify the equation as a conditional equation, an identity, or a contradiction and then state the solution:

identity; all real numbers

EXAMPLE 10

Classify as a conditional equation, an identity, or a contradiction. Then state the solution.

Solution

Given equation.

Distribute and combine like terms.

Divide by and simplify.

The equation is true when

This is a conditional equation.
The solution is .

TRY IT 10.1

Classify the equation as a conditional equation, an identity, or a contradiction and then state the solution:

conditional equation;

TRY IT 10.2

Classify the equation as a conditional equation, an identity, or a contradiction and then state the solution:

conditional equation;

EXAMPLE 11

Classify the equation as a conditional equation, an identity, or a contradiction. Then state the solution.

Solution

Given equation.

Distribute.

Combine like terms.

Subtract from both sides.

Simplify.

But .

It has no solution.

TRY IT 11.1

Classify the equation as a conditional equation, an identity, or a contradiction and then state the solution:

TRY IT 11.2

Classify the equation as a conditional equation, an identity, or a contradiction and then state the solution:

Type of equation – Solution

Type of equation What happens when you solve it? Solution
Conditional Equation True for one or more values of the variables and false for all other values One or more values
Identity True for any value of the variable All real numbers
Contradiction False for all values of the variable No solution

# Key Concepts

• General Strategy for Solving Linear Equations
1. Simplify each side of the equation as much as possible.
Use the Distributive Property to remove any parentheses.
Combine like terms.
2. Collect all the variable terms on one side of the equation.
Use the Addition or Subtraction Property of Equality.
3. Collect all the constant terms on the other side of the equation.
Use the Addition or Subtraction Property of Equality.
4. Make the coefficient of the variable term to equal to 1.
Use the Multiplication or Division Property of Equality.
State the solution to the equation.
5. Check the solution.
Substitute the solution into the original equation.

# Glossary

conditional equation
An equation that is true for one or more values of the variable and false for all other values of the variable is a conditional equation.
An equation that is false for all values of the variable is called a contradiction. A contradiction has no solution.
identity
An equation that is true for any value of the variable is called an identity. The solution of an identity is all real numbers.

# Practice Makes Perfect

## Solve Equations Using the General Strategy for Solving Linear Equations

In the following exercises, solve each linear equation.

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58

## Classify Equations

In the following exercises, classify each equation as a conditional equation, an identity, or a contradiction and then state the solution.

 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78

### Everyday Math

 79. Coins. Rhonda has \$1.90 in nickels and dimes. The number of dimes is one less than twice the number of nickels. Find the number of nickels, n, by solving the equation . 80. Fencing. Micah has 44 feet of fencing to make a dog run in his yard. He wants the length to be 2.5 feet more than the width. Find the length, L, by solving the equation .

### Writing Exercises

 81. Explain why you should simplify both sides of an equation as much as possible before collecting the variable terms to one side and the constant terms to the other side. 82. Using your own words, list the steps in the general strategy for solving linear equations. 83. Solve the equation explaining all the steps of your solution as in the examples in this section. 84. What is the first step you take when solving the equation ? Why is this your first step?