High School Math : Inequalities

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #231 : Algebra Ii

Solve for \displaystyle x:

\displaystyle \frac{-7x-2}{3}>11

Possible Answers:

\displaystyle x< -5

\displaystyle x>-3

\displaystyle x>2

\displaystyle x< 7

\displaystyle x>-5

Correct answer:

\displaystyle x< -5

Explanation:

Inequalities can be treated like any other equation except when multiplying and dividing by negative numbers. When multiplying or dividing by negative numbers, we just flip the sign of the inequality so that \displaystyle > becomes \displaystyle < , and vice versa.

\displaystyle \frac{-7x-2}{3}>11

\displaystyle -7x-2>33

\displaystyle -7x>35

\displaystyle \frac{-7x}{-7}< \frac{35}{-7}

\displaystyle x< -5

Example Question #232 : Algebra Ii

Solve for \displaystyle x:

\displaystyle x^2+4x>12

Possible Answers:

\displaystyle x< -12

\displaystyle x< -6\ and\ x>2

\displaystyle x< -2\ and\ x>6

\displaystyle x>2

\displaystyle x< 6

Correct answer:

\displaystyle x< -6\ and\ x>2

Explanation:

Inequalities can be treated like any other equation except when multiplying and dividing by negative numbers. When multiplying or dividing by negative numbers, we just flip the sign of the inequality so that \displaystyle > becomes \displaystyle < , and vice versa. When we solve binomials, we must take extra caution because \displaystyle (-x)^2=x^2.

So when we solve inequalities with binomials, we must create two scenarios: one where the value inside of the parentheses is positive and one where it is negative. For the negative scenario, we must flip the sign as we normally do for inequalities.

\displaystyle x^2+4x>12

\displaystyle x^2+4x+4>12+4

\displaystyle (x+2)^2>16

Now we must create our two scenarios:

\displaystyle x+2>{\sqrt{16}} and \displaystyle x+2< -{\sqrt{16}}

Notice that in the negative scenario, we flipped the sign of the inequality.

\displaystyle x+2>4 and \displaystyle x+2< -4

\displaystyle x>2 and \displaystyle x< -6

Example Question #2 : Inequalities

Solve for \displaystyle x:

\displaystyle x^2-10x< 24

Possible Answers:

\displaystyle x< -12

\displaystyle x>5

\displaystyle x>-2\ and\ x< 12

\displaystyle x< 5\ and\ x>10

\displaystyle x>0\ and\ x< 2

Correct answer:

\displaystyle x>-2\ and\ x< 12

Explanation:

Inequalities can be treated like any other equation except when multiplying and dividing by negative numbers. When multiplying or dividing by negative numbers, we just flip the sign of the inequality so that \displaystyle > becomes \displaystyle < , and vice versa. When we solve binomials, we must take extra caution because \displaystyle (-x)^2=x^2.

So when we solve inequalities with binomials, we must create two scenarios: one where the value inside of the parentheses is positive and one where it is negative. For the negative scenario, we must flip the sign as we normally do for inequalities.

\displaystyle x^2-10x< 24

\displaystyle x^2-10x+25< 24+25

\displaystyle (x-5)^2< 49

Now we must create our two scenarios:

\displaystyle x-5< {\sqrt{49}} and \displaystyle x-5>-{\sqrt{49}}

Notice that in the negative scenario, we flipped the sign of the inequality.

\displaystyle x-5< 7 and \displaystyle x-5>-7

\displaystyle x< 12 and \displaystyle x>-2

Example Question #1 : Inequalities

Solve the inequality for x:

\displaystyle 2x+4>64

Possible Answers:

\displaystyle x>28

\displaystyle x>30

\displaystyle x=30

\displaystyle x< 28

\displaystyle x< 30

Correct answer:

\displaystyle x>30

Explanation:

\displaystyle 2x+4>64

Subtract 4 from both sides:

\displaystyle 2x > 60

Divide both sides by 2:

\displaystyle x > 30

Example Question #1 : Solving Inequalities

Solve for \displaystyle x.

\displaystyle -7x-4\geq10

Possible Answers:

\displaystyle x\geq2

\displaystyle x\geq-2

\displaystyle x\leq2

\displaystyle x\leq-2

Correct answer:

\displaystyle x\leq-2

Explanation:

\displaystyle -7x-4\geq10

Add 4 to both sides.

\displaystyle -7x\geq14

Divide both sides by –7. When dividing by a negative value, we must also change the direction of the inequality sign.

\displaystyle x\leq-2

Example Question #1 : Solving Inequalities

Solve for \displaystyle x:

\displaystyle 9x-27\geq6x

Possible Answers:

\displaystyle x\leq9

\displaystyle x\geq3

\displaystyle x\leq3

\displaystyle x\geq9

\displaystyle x>9

Correct answer:

\displaystyle x\geq9

Explanation:

\displaystyle 9x-27\geq6x

Move like terms to the same sides:

\displaystyle 9x-6x\geq27

Combine like terms:

\displaystyle 3x\geq27

Divide both sides by 3:

\displaystyle x\geq9

Example Question #2 : Solving Inequalities

Solve for \displaystyle x:

\displaystyle 5-3x\leq14

Possible Answers:

\displaystyle x\geq9

\displaystyle x\leq3

\displaystyle x\geq-3

\displaystyle x\geq0

\displaystyle x\geq3

Correct answer:

\displaystyle x\geq-3

Explanation:

Inequalities can be treated like any other equation except when multiplying and dividing by negative numbers. When multiplying or dividing by negative numbers, we just flip the sign of the inequality so that \displaystyle > becomes \displaystyle < , and vice versa.

\displaystyle 5-3x\leq14

\displaystyle -3x\leq9

\displaystyle \frac{-3x}{-3}\geq\frac{9}{-3}

\displaystyle x\geq-3

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