Solving Multi-Step Equations

Most equations will require two or more steps to solve. The steps used when solving two-step equations are still inverse operations and the Properties of Equality. When solving, begin as far away from the variable as possible. Consider the following equation. $2x-1=7$

Notice that the variable is undergoing two operations. Namely, it is multiplied by 2, then decreased by 1. Both operations must be undone to isolate

x.

Solve the two-step equation

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Exercise

Solve $2x-1=7.$

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Solution

To solve the equation, we will add

1

to both sides, then divide by

2.

2x-1=7

\text{LHS}+1=\text{RHS}+1

2x-1+1=7+1

Add terms

2x=8

\left.\text{LHS}\middle/2\right.=\left.\text{RHS}\middle/2\right.

\dfrac{2x}{2}=\dfrac{8}{2}

Simplify quotient

x=4

Now that

x

has been isolated, we can see that the solution is

x=4.

Concept

Multi-Step Equations

In addition to requiring more than one step, some equations contain distinct elements. Below are examples of each.

\begin{aligned} \textbf{Combining Like Terms:} & \quad 6=5x+2x-8 \\ \textbf{Variable Terms on Both Sides:} & \quad x+1=\text{-} 5x-5\\ \textbf{Distributive Property:} & \quad 4(\text{-} 6x+3)=12 \end{aligned}

Concept

Combining Like Terms

When simplifying algebraic expressions, it is only possible to combine (add or subtract) like terms. $\begin{gathered} 7y+2x-3y-2+x+5 \end{gathered}$ This example expression contains three sets of like terms: $x\text{-terms},$ $y\text{-terms},$ and $\text{constants}.$

To simplify the expression, the terms should first be rearranged such that like terms are grouped together. Then, the like terms can be combined by adding or subtracting the constants as well as adding or subtracting the coefficients of the variables.

\begin{aligned} \colorbox{#99ffbb}{$+7y-3y$} &\quad + & \colorbox{#b3e6ff}{$+2x+x$} &\quad + & \colorbox{#ffb3b3}{$\text{-}2+5$} \\ {\color{#009600}{4y}} \quad\ &\quad + & {\color{#0000FF}{3x}} \quad\ &\quad + & {\color{#FF0000}{3}}\quad \end{aligned}

Solve the equation by combining like terms

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Exercise

Solve $6=5x+2x-8.$

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Solution

Notice there are two

x

-terms on the right-hand side of the equation. To begin, we will combine these terms.

6=5x+2x-8

Add terms

6=7x-8

From here, we can solve the equation using inverse operations to isolate

x.

Specifically, we can add

8

to both sides, then divide by

7.

6=7x-8

\text{LHS}+8=\text{RHS}+8

6+8=7x-8+8

Add terms

14=7x

\left.\text{LHS}\middle/7\right.=\left.\text{RHS}\middle/7\right.

\dfrac{14}{7}=\dfrac{7x}{7}

Simplify quotient

2=x

Rearrange equation

x=2

The equation has the solution

x=2.

Concept

Variables on Both Sides

When an equation has variable terms on both sides, it is necessary to transfer them to one side using inverse operations. Once all variable terms are on the same side, they can be combined.

\begin{aligned} 3x&=x-2\\ 3x{\color{#0000FF}{-x}}&=x{\color{#0000FF}{-x}}-2\\ 2x&=\text{-} 2 \end{aligned}

Solve the equation with variables on both sides

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Exercise

Solve $x+1=\text{-} 5x-5.$

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Solution

Notice in the equation that there are two variable terms —

x

on the left-hand side and

\text{-} 5x

on the right. We need to move one of these terms to the other side, it does not matter which. Let's move

\text{-} 5x

to the left by adding

5x

to the equation (the inverse operation of subtracting

5

). After that, we can combine like terms.

x+1=\text{-} 5x-5

\text{LHS}+5x=\text{RHS}+5x

x+1+5x=\text{-} 5x-5+5x

Simplify terms

6x+1=\text{-} 5

From here, we can isolate

x

by subtracting

1

then dividing by

6

on both sides.

6x+1=\text{-} 5

\text{LHS}-1=\text{RHS}-1

6x+1-1=\text{-} 5-1

Subtract terms

6x=\text{-} 6

\left.\text{LHS}\middle/6\right.=\left.\text{RHS}\middle/6\right.

\dfrac{6x}{6}=\dfrac{\text{-} 6}{6}

Simplify quotient

x=\text{-} 1

The equation has the solution

x=\text{-} 1.

Rule

Distributive Property

The Distributive Property can be used to simplify expressions with parentheses. The factor outside the parentheses is multiplied, or distributed, to every term inside.

Use the Distributive Property to solve the equation

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Exercise

Solve $4(\text{-} 6x+3)=12.$

Show Solution

Solution

To solve the equation for

x,

we must first distribute

4

into the parentheses.

4(\text{-} 6x+3)=12

Distribute

4

4(\text{-} 6x)+4\cdot 3=12

Multiply

\text{-} 24x+12=12

From here, we can subtract

12

then divide by

\text{-} 24

to isolate

x.

\text{-} 24x+12=12

\text{LHS}-12=\text{RHS}-12

\text{-} 24x+12-12=12-12

Subtract term

\text{-} 24x=0

\left.\text{LHS}\middle/\text{-} 24\right.=\left.\text{RHS}\middle/\text{-} 24\right.

\dfrac{\text{-} 24x}{\text{-} 24}=\dfrac{0}{\text{-} 24}

Simplify quotient

x=0

The equation has the solution

x=0.

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Formulary

Course 1

Course 2

Course 3

Course 4

Course 5

Solving Multi-Step Equations

Example

Solve the two-step equation

Multi-Step Equations

Combining Like Terms

Example

Solve the equation by combining like terms

Variables on Both Sides

Example

Solve the equation with variables on both sides

Distributive Property

Example

Use the Distributive Property to solve the equation