Solving One-Step Equations

An equation is a statement of equality. The quantity on the left-hand side is equal to the quantity on the right-hand side. Solving an equation means finding the value of the variable that makes the statement true. This is done by isolating the variable on one side of the equation, through the use of inverse operations and the Properties of Equality.

Concept

Inverse Operations

Inverse operations are two operations that undo each other. For instance, adding $2$ and subtracting $2$ are inverse operations because they cancel each other out. These can be used to eliminate parts of an expression or equation. In an expression such as $x + 6,$ the $6$ can be eliminated by performing the inverse operation of adding $6,$ which is subtracting $6.$ $\begin{gathered} x+6\,{\color{#0000FF}{-}}\,{\color{#0000FF}{6}}=x \end{gathered}$

When using inverse operations on an equation, it is important to perform the same operation on each side to maintain equality. The result will then be an equivalent equation, which is an equation that retains the same solution.

Concept

Addition and Subtraction Properties of Equality

The Addition Property of Equality states that adding the same number to each side of an equation yields an equivalent equation.

If

a = b,

then

a + c = b + c.

The Subtraction Property of Equality is similar to the Addition one, with the exception being the sign used — subtracting the same number from each side of an equation yields an equivalent equation.

If

a = b,

then

a - c = b - c.

Either of these properties can be used when eliminating a term in an equation. Deciding which to use depends on if the term is being added to or subtracted from the variable.

Misc Addition and Subtraction Property of Equality 1.svg

Solve the equation with the Addition or Subtraction Property of Equality

Exercise

Solve the following equations. $x - 4 = 9 \quad \text{and} \quad x + 5 = 3$

Solution

Example

$x - 4 = 9$

To solve this equation, we have to isolate the variable $x.$ For this, we can eliminate the term being subtracted from $x$ by performing the inverse operation. Since the inverse operation of subtracting $4$ is adding $4,$ we'll add $4$ to each side of the equation. In line with the Addition Property of Equality, this produces an equivalent equation.

x - 4 = 9

\text{LHS}+4=\text{RHS}+4

x - 4 + 4 = 9 + 4

Add terms

x = 13

Thus, the solution to the equation is $x = 13.$

Example

$x + 5 = 3$

Here, the $+5$ has to be eliminated for us to isolate $x.$ The inverse operation of adding $5$ is subtracting $5.$ Thus, we'll subtract $5$ from each side of the equation. By the Subtraction Property of Equality, this yields an equivalent equation.

x + 5 = 3

\text{LHS}-5=\text{RHS}-5

x + 5 - 5 = 3 - 5

Subtract terms

x = \text{-} 2

$x = \text{-} 2$ is the solution of the equation.

Show solution

Concept

Multiplication and Division Properties of Equality

The Multiplication Property of Equality states that multiplying each side of an equation by the same number yields an equivalent equation.

If

a = b,

then

a \cdot c = b \cdot c.

Similarly, by the Division Property of Equality, an equivalent equation is produced when each side of an equation is divided by the same non-zero number.

If

a = b

and

c \neq 0,

then

\dfrac{a}{c} = \dfrac{b}{c}.

These two properties can be used when solving equations to eliminate denominators and factors, since multiplication is the inverse operation of division and vice versa.

Misc Multiplication and Division Property of Equality 1.svg

Solve the equation with the Multiplication or Division Property of Equality

Exercise

Solve the following equations. $\dfrac{a}{3} = 7 \quad \text{and} \quad 11b = 22.$

Solution

Example

$\dfrac{a}{3} = 7$

To isolate the variable $a,$ we have to eliminate the denominator $3.$ For this we can use the inverse operation of division, which is multiplication. According to the Multiplication Property of Equality, multiplying each side of the equation by $3$ will produce an equivalent equation. Notice that it will also eliminate the denominator.

\dfrac{a}{3} = 7

\text{LHS} \cdot 3=\text{RHS}\cdot 3

\dfrac{a}{3} \cdot 3 = 7 \cdot 3

Multiply

a = 21

We have found that $a = 21$ solves the equation.

Example

$11b = 22$

Since division is the inverse operation of multiplication, we'll use the Division Property of Equality to eliminate the factor $11.$ This is done by dividing each side of the equation by $11.$

11b = 22

\left.\text{LHS}\middle/11\right.=\left.\text{RHS}\middle/11\right.

\dfrac{11b}{11} = \dfrac{22}{11}

Simplify quotient

b = 2

The solution of the equation is $b = 2.$

Show solution

Solving One-Step Equations

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Inverse Operations

Addition and Subtraction Properties of Equality

Example

Solve the equation with the Addition or Subtraction Property of Equality

$x - 4 = 9$

$x + 5 = 3$

Multiplication and Division Properties of Equality

Example

Solve the equation with the Multiplication or Division Property of Equality

$\dfrac{a}{3} = 7$

$11b = 22$

Exercises

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Solution

One-Variable Equations

Example

Solve the equation with the Addition or Subtraction Property of Equality

Example

Solve the equation with the Multiplication or Division Property of Equality

Exercises

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Solution