Algebra II : Solving Inequalities

Study concepts, example questions & explanations for Algebra II

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Example Questions

Example Question #131 : Inequalities

Solve the inequality:  \displaystyle 2(3-2x)\leq 9(2-3x)

Possible Answers:

\displaystyle x\geq \frac{12}{31}

\displaystyle x\geq -\frac{12}{23}

\displaystyle x\leq \frac{12}{23}

\displaystyle x\leq -\frac{12}{23}

\displaystyle x\geq \frac{12}{23}

Correct answer:

\displaystyle x\leq \frac{12}{23}

Explanation:

Use the distributive property to simplify the binomials.

\displaystyle 2(3)-2(2x)\leq 9(2)-9(3x)

Simplify both sides.

\displaystyle 6-4x\leq 18-27x

Add \displaystyle 27x on both sides.

\displaystyle 6-4x+27x\leq 18-27x+27x

\displaystyle 6+23x\leq 18

Subtract six from both sides.

\displaystyle 6+23x-6\leq 18-6

\displaystyle 23x\leq 12

Divide by 23 on both sides.

\displaystyle \frac{23x}{23}\leq \frac{12}{23}

The answer is:  \displaystyle x\leq \frac{12}{23}

Example Question #2163 : Algebra Ii

Solve:  \displaystyle 3x>-5(2x-3)

Possible Answers:

\displaystyle x>-\frac{15}{7}

\displaystyle x>\frac{15}{13}

\displaystyle x>-\frac{13}{15}

\displaystyle x>\frac{15}{7}

\displaystyle x>-\frac{15}{13}

Correct answer:

\displaystyle x>\frac{15}{13}

Explanation:

Use distribution to simplify the right side.

\displaystyle 3x>-5(2x)-5(-3)

Simplify the right side.

\displaystyle 3x>-10x+15

Add \displaystyle 10x on both sides of the equation.

\displaystyle 3x+10x>-10x+15+10x

\displaystyle 13x>15

Divide by 13 on both sides.

\displaystyle \frac{13x}{13}>\frac{15}{13}

The answer is:  \displaystyle x>\frac{15}{13}

Example Question #2164 : Algebra Ii

Solve:  \displaystyle 2-4x>6x-8

Possible Answers:

\displaystyle x>5

\displaystyle x>1

\displaystyle x< -5

\displaystyle x< 1

\displaystyle x< 5

Correct answer:

\displaystyle x< 1

Explanation:

Add \displaystyle 4x on both sides.

\displaystyle 2-4x+4x>6x-8+4x

\displaystyle 2>10x-8

Add 8 on both sides.

\displaystyle 2+8>10x-8+8

\displaystyle 10>10x

Divide by 10 on both sides.

\displaystyle \frac{10}{10}>\frac{10x}{10}

\displaystyle 1>x

The answer is:  \displaystyle x< 1

Example Question #2165 : Algebra Ii

Solve the inequality:  \displaystyle -9x+7>8+9x

Possible Answers:

\displaystyle x>-\frac{15}{18}

\displaystyle x< -\frac{1}{18}

\displaystyle x< -\frac{15}{18}

\displaystyle x>-\frac{1}{18}

Correct answer:

\displaystyle x< -\frac{1}{18}

Explanation:

Add \displaystyle 9x on both sides to avoid dividing by a negative later in the calculation.  Dividing by a negative value will require switching the sign.

\displaystyle -9x+7+(9x)>8+9x+(9x)

The inequality becomes:  

\displaystyle 7> 18x+8

Subtract 8 from both sides.

\displaystyle 7-8> 18x+8-8

\displaystyle -1>18x

Divide by 18 on both sides.

\displaystyle \frac{-1}{18}>\frac{18x}{18}

The answer is:  \displaystyle x< -\frac{1}{18}

Example Question #95 : Solving Inequalities

Solve the inequality:  \displaystyle \sqrt{5x-7}< \sqrt{2x}

Possible Answers:

\displaystyle (-\infty,\frac{7}{3})

\displaystyle (0,\frac{7}{3})

\displaystyle [\frac{7}{5},\frac{7}{3})

\displaystyle (0,\frac{7}{5}]

\displaystyle (\frac{7}{5},\frac{7}{3})

Correct answer:

\displaystyle [\frac{7}{5},\frac{7}{3})

Explanation:

There is a domain restriction with the square root functions.

Both the functions must be zero or greater.

Square both sides.

\displaystyle (\sqrt{5x-7}) ^2< (\sqrt{2x})^2

\displaystyle 5x-7< 2x

Subtract \displaystyle 2x from both sides, and add 7 on both sides.

\displaystyle 5x-7+(7)-[2x]< 2x-[2x]+(7)

\displaystyle 3x< 7

Divide by three on both sides to isolate x.

\displaystyle x< \frac{7}{3}

Notice that this value will also include all the values that are negative, which cannot satisfy the original equation.  We will need to identify the largest possible x-value of both radicals to determine a viable domain.

Set the two radicals greater or equal to zero and solve for \displaystyle x.

\displaystyle \sqrt{2x}\geq0 \rightarrow 2x\geq 0 \rightarrow x\geq0

\displaystyle \sqrt{5x-7}\geq0 \rightarrow5x-7\geq0 \rightarrow 5x\geq7\rightarrow x\geq \frac{7}{5}

The value of \displaystyle x must also be greater than \displaystyle \frac{7}{5}.

Rewrite \displaystyle \frac{7}{5}\leq x< \frac{7}{3} in interval notation.

The answer is:  \displaystyle [\frac{7}{5},\frac{7}{3})

Example Question #91 : Solving Inequalities

Solve:  \displaystyle 2x^2>18

Possible Answers:

\displaystyle (-\infty, 3) \bigcup(3,\infty)

\displaystyle (-3,3)

\displaystyle (-\infty, -3) \bigcup(3,\infty)

\displaystyle (-\infty, -3] \bigcup[3,\infty)

\displaystyle [-3,3]

Correct answer:

\displaystyle (-\infty, -3) \bigcup(3,\infty)

Explanation:

Divide by two on both sides.

\displaystyle \frac{2x^2}{2}>\frac{18}{2}

The inequality becomes:

\displaystyle x^2>9

Square root both sides.

\displaystyle \sqrt{x^2}>\sqrt{9}

\displaystyle \pm x >3

Split the inequalities.

\displaystyle x>3 is one solution.

Simplify \displaystyle -x>3 by dividing by negative one on both sides.  This will change the sign.

\displaystyle \frac{-x}{-1}>\frac{3}{-1}

\displaystyle x< -3 is the second solution.

Write the terms in interval notation.

The answer is:  \displaystyle (-\infty, -3) \bigcup(3,\infty)

Example Question #92 : Solving Inequalities

Solve:  \displaystyle -3x+7\leq 8x-4

Possible Answers:

\displaystyle x\geq \frac{3}{11}

\displaystyle x\geq1

\displaystyle x\leq1

\displaystyle x\leq-1

Correct answer:

\displaystyle x\geq1

Explanation:

Add \displaystyle 3x on both sides.

\displaystyle -3x+7+(3x)\leq 8x-4+(3x)

\displaystyle 7\leq 11x-4

Add four on both sides.

\displaystyle 7+4\leq 11x-4+4

\displaystyle 11\leq 11x

Divide by eleven on both sides.

\displaystyle \frac{11}{11}\leq \frac{11x}{11}

\displaystyle 1\leq x

The answer is:  \displaystyle x\geq1

Example Question #93 : Solving Inequalities

Solve:   \displaystyle -3x-8< -4x-9

Possible Answers:

\displaystyle x>-17

\displaystyle x< -\frac{7}{17}

\displaystyle x< -1

\displaystyle x\leq-1

\displaystyle x< -17

Correct answer:

\displaystyle x< -1

Explanation:

Add \displaystyle 4x on both sides.

\displaystyle -3x-8+4x< -4x-9+4x

\displaystyle x-8< -9

Add eight on both sides.

\displaystyle x-8+8< -9+8

Simplify both sides.

The answer is:  \displaystyle x< -1

Example Question #94 : Solving Inequalities

Solve:  \displaystyle -8(2x-3)< 17

Possible Answers:

\displaystyle x>-\frac{41}{16}

\displaystyle x< \frac{41}{16}

\displaystyle x>\frac{41}{16}

\displaystyle x< \frac{7}{16}

\displaystyle x>\frac{7}{16}

Correct answer:

\displaystyle x< \frac{7}{16}

Explanation:

Distribute the negative eight into the binomial.

\displaystyle -16x+24< 17

Subtract 24 on both sides.

\displaystyle -16x+24-24< 17-24

\displaystyle -16x< -7

Divide by negative 16 on both sides.  The sign will change direction since we are dividing by a negative value.

\displaystyle \frac{-16x}{-16}< \frac{-7}{-16}

The answer is:  \displaystyle x< \frac{7}{16}

Example Question #95 : Solving Inequalities

Solve:  \displaystyle -3(3x-8)>9x+7

Possible Answers:

\displaystyle x< -\frac{31}{18}

\displaystyle x>\frac{31}{18}

\displaystyle x>\frac{17}{18}

\displaystyle x< \frac{17}{18}

\displaystyle x< \frac{31}{18}

Correct answer:

\displaystyle x< \frac{17}{18}

Explanation:

Distribute the negative three through both terms of the binomial.

\displaystyle -9x+24>9x+7

Add \displaystyle 9x on both sides.

\displaystyle -9x+24+9x>9x+7+9x

\displaystyle 24>18x+7

Subtract seven on both sides.

\displaystyle 24-7>18x+7-7

\displaystyle 17>18x

Divide by 18 on both sides.

\displaystyle \frac{17}{18}>\frac{18x}{18}

The answer is:  \displaystyle x< \frac{17}{18}

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