Suppose that we wish to find the solution to the inequality

2x + 6 < 12.

An inequality like this one can be solved just like an equation, using the addition and multiplication principles.

First, we apply the addition principle, subtracting 6 from both sides:

\begin{align*} 2x + 6 &\lt 12 \\[5pt] 2x+6-6 &\lt 12-6 \\[5pt] 2x+0 &\lt 6 \\[5pt] 2x &\lt 6 \end{align*}

Second, we apply the multiplication principle, dividing both sides by 2{:}

\begin{align*} \require{cancel} 2x &\lt 6 \\[5pt] \dfrac{2x}{2} &\lt \dfrac62 \\[5pt] \dfrac{\cancel{2}x}{\cancel{2}} &\lt 3 \\[5pt] x &\lt 3 \end{align*}

The solution is x < 3 In other words, any value less than 3 satisfies the inequality.

Let's see another example.

FLAG

Solve the inequality 10x - 4 > 16.

EXPLANATION

First, we apply the addition principle, adding 4 to both sides:

\begin{align*} 10x-4 &> 16 \\[5pt] 10x-4+4 &>16+4\\[5pt] 10x+0 &>20 \\[5pt] 10x &>20 \end{align*}

Second, we apply the multiplication principle, dividing both sides by 10{:}

\begin{align*} \require{cancel} 10x &>20 \\[5pt] \dfrac{10x}{10} &> \dfrac{20}{10} \\[5pt] \dfrac{\cancel{10}x}{\cancel{10}} &> 2 \\[5pt] x &> 2 \end{align*}

Therefore, the solution is x> 2.

FLAG

Solve the inequality $3x - 5 \le 4.$

a
$x \le 4$
b
$x \ge 3$
c
$x \ge -4$
d
$x \le 3$
e
$x \ge 4$

Solve the inequality $3c+1 \le 0.$

a
$c \ge -\dfrac{1}{3}$
b
$c \le -\dfrac{1}{3}$
c
$c \ge \dfrac{1}{3}$
d
$c \ge \dfrac{2}{3}$
e
$c \le \dfrac{2}{3}$

Solve the inequality $4t - 30 > - 20.$

a
$t < 10$
b
$t > \dfrac{5}{2}$
c
$t > \dfrac{4}{5}$
d
$t < \dfrac{5}{2}$
e
$t < \dfrac{3}{4}$

Solve the inequality -2x + 3 > -1.

EXPLANATION

First, we apply the addition principle, subtracting 3 from both sides: \begin{align} -2x + 3 &> -1 \\[5pt] -2x + 3 - 3 &> -1 - 3 \\[5pt] -2x + 0 &> -4 \\[5pt] -2x &> -4 \end{align}

Then, we apply the multiplication principle, dividing both sides by -2.

Remember, when multiplying or dividing an inequality by a negative number, we need to flip the inequality sign:

\begin{align} \require{cancel} -2x \,\,&{\color{blue}>\,\,} -4 \\[5pt] \dfrac{-2x}{-2} \,&{\color{red}<\,\,} \dfrac{-4}{-2} \\[5pt] \dfrac{\cancel{-2}x}{\cancel{-2}} \,&{\color{red}<\,\,} {2} \\[5pt] x \,\,&{\color{red}<\,\,} {2} \end{align}

Therefore, the solution is x<2.

FLAG

Solve the inequality $-2x + 3 \le 7.$

a
$x \le -2$
b
$x \le 4$
c
$x \ge 2$
d
$x \geq 4$
e
$x \ge -2$

Solve the inequality $ -6x - 5 \geq -8.$

a
$x\ge \dfrac {1} {2}$
b
$x\ge \dfrac {1} {3}$
c
$x\le \dfrac {1} {2}$
d
$x\le -\dfrac {1} {2}$
e
$x\le \dfrac {1} {3}$

Solve the inequality $-5x + 6 > -9.$

a
$x < -5$
b
$x > 3$
c
$x < -3$
d
$x < 3$
e
$x > 5$

Solve the inequality -11 \le -8y + 5.

EXPLANATION

First, we apply the addition principle, subtracting 5 from both sides:

\begin{align} -11 &\le -8y + 5 \\[5pt] -11-5 &\le -8y +5-5 \\[5pt] -16 &\le -8y + 0 \\[5pt] -16 &\le -8y \end{align}

Then, we apply the multiplication principle, dividing both sides by -8.

Remember, when multiplying or dividing an inequality by a negative number, we need to flip the inequality sign:

\begin{align} \require{cancel} -16 \,\,&{\color{blue}\le \,\,} {-8y} \\[5pt] \dfrac{-16}{-8} \,&{\color{red}\ge\,\,} \dfrac {-8y}{-8} \\[5pt] 2 \,&{\color{red}\ge\,\,} \dfrac {\cancel{-8}y}{\cancel{-8}} \\[5pt] 2 \,&{\color{red}\ge\,\,} y \end{align}

Finally, let's swap the left and right-hand sides so that the variable is on the left-hand side. Remember, we also need to flip the inequality.

y \le 2

Therefore, the solution is y \le 2.

FLAG

Solve the inequality $-5 \lt 6w+7.$

a
$w \gt 2$
b
$w \lt \dfrac12$
c
$w \lt -2$
d
$w \gt -2$
e
$w \lt 2$

Solve the inequality $6 < -2y + 7.$

a
$y < \dfrac12$
b
$y < -\dfrac12$
c
$y \lt -2$
d
$y > \dfrac12$
e
$y > 2$

Solve the inequality $-8 > 4y + 12.$

a
$y < -5$
b
$y < 5$
c
$y > -1$
d
$y < -1$
e
$y > -5$
Flag Content
Did you notice an error, or do you simply believe that something could be improved? Please explain below.
SUBMIT
CANCEL