College Algebra : Linear Inequalities

Study concepts, example questions & explanations for College Algebra

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Example Questions

Example Question #1 : Linear Inequalities

Solve the following inequality.

\(\displaystyle 2x-8>10\).

Possible Answers:

\(\displaystyle x\geq -9\)

\(\displaystyle x< 9\)

\(\displaystyle x\leq 18\)

\(\displaystyle x>18\)

\(\displaystyle x>9\)

Correct answer:

\(\displaystyle x>9\)

Explanation:

To solve this inequality, we treat is a a regular equation. First, we add 8 to both sides.

\(\displaystyle 2x>18\).

We now divide both sides by 2 to get 

\(\displaystyle x>9\).

Example Question #2 : Linear Inequalities

Solve:  \(\displaystyle 5x\leq-\frac{3}{5}\)

Possible Answers:

\(\displaystyle x \geq -3\)

\(\displaystyle x \leq -\frac{3}{25}\)

\(\displaystyle x \leq -3\)

\(\displaystyle x \geq -\frac{3}{25}\)

\(\displaystyle x \leq \frac{3}{25}\)

Correct answer:

\(\displaystyle x \leq -\frac{3}{25}\)

Explanation:

To evaluate, we will need to multiply both sides by one-fifth.

\(\displaystyle 5x\cdot \frac{1}{5}\leq-\frac{3}{5}\cdot\frac{1}{5}\)

The sign does not need to be switched unless we multiply or divide by a negative value.

The answer is:  \(\displaystyle x \leq -\frac{3}{25}\)

Example Question #61 : Solving Equations And Inequallities

Express the following linear inequality in interval notation.

\(\displaystyle 6x+3>4x-1\)

Possible Answers:

\(\displaystyle \left ( 2,\infty \right )\)

\(\displaystyle \left ( -\infty ,-2\right )\)

\(\displaystyle \left ( -2,\infty \right )\)

\(\displaystyle (-\infty ,2)\)

\(\displaystyle \left [ -2,\infty \right ]\)

Correct answer:

\(\displaystyle \left ( -2,\infty \right )\)

Explanation:

Upon solving for x, we find that x is larger than -2.  The left-hand term of the interval is -2 since it is the lower bound for our set, and it has a parenthesis around it because it is not included in our set (-2 is not greater than -2).  The right-hand term of the interval is positive infinity because any number larger than -2 is in the set.  There is always a parenthesis around infinity or negative infinity.

Example Question #62 : Solving Equations And Inequallities

Express the following linear inequality in interval notation.

\(\displaystyle x+7\geq4x-8\)

Possible Answers:

\(\displaystyle (-\infty ,5]\)

\(\displaystyle \left ( -\infty ,5\right )\)

\(\displaystyle [5,\infty )\)

\(\displaystyle (-\infty ,-5)\)

\(\displaystyle (-\infty ,-5]\)

Correct answer:

\(\displaystyle (-\infty ,5]\)

Explanation:

Upon solving for x, we find that x is less than or equal to 5.  The left-hand term of the interval is negative infinity since any number less than 5 is in our set, and infinity always has a parenthesis around it.  The right-hand term of the interval is 5 since it is the upper bound of our set.  There is a bracket around it because 5 is included in our set (5 is less than or equal to 5).

Example Question #63 : Solving Equations And Inequallities

Express the following linear inequality in interval notation.

 

\(\displaystyle (x+1)(x+2)>x(x+1)\)

Possible Answers:

\(\displaystyle (-\infty ,1)\)

\(\displaystyle [-1,\infty )\)

\(\displaystyle (-\infty ,-1)\)

\(\displaystyle \left ( -1,\infty \right )\)

\(\displaystyle (-\infty ,1]\)

Correct answer:

\(\displaystyle \left ( -1,\infty \right )\)

Explanation:

Upon expanding and solving for x, we find that x is greater than -1.  The left-hand term of the interval is -1 since it is the lower bound of our set, and has a parenthesis around it because it is not in our set (-1 is not greater than -1).  The right-hand term of the interval is infinity because any number larger than -1 is in our set, and there is always a parenthesis around infinity.

Example Question #64 : Solving Equations And Inequallities

Express the following linear inequality in interval notation.

\(\displaystyle 5\leq x-3\leq7\)

Possible Answers:

\(\displaystyle [8,10]\)

\(\displaystyle (8,10]\)

\(\displaystyle \left ( 8,10\right )\)

\(\displaystyle (2,4)\)

\(\displaystyle [2,4]\)

Correct answer:

\(\displaystyle [8,10]\)

Explanation:

Upon solving for x, we find that 8 is less than or equal to x which is less than or equal to 10, or x is greater than or equal to 8 AND x is less than or equal to 10.  The left-hand term of our interval is 8 since it is the lower bound for our set, and there is a bracket around it since it is in our set (8 is greater than or equal to 8).  The right-hand term of our interval is 10 since it is the upper bound for our set, and there is also a bracket around it since it is in our set (10 is less than or equal to 10).

Example Question #65 : Solving Equations And Inequallities

Express the following linear inequality in interval notation.

\(\displaystyle -4\leq6-2x< 4\)

Possible Answers:

\(\displaystyle (1,5]\)

\(\displaystyle (-1,-5)\)

\(\displaystyle (-5,-1)\)

\(\displaystyle (1,5)\)

\(\displaystyle [1,5]\)

Correct answer:

\(\displaystyle (1,5]\)

Explanation:

Upon solving for x, we find that 1 is less than x which is less than or equal to 5, or x is greater than 1 AND x is less than or equal to 5.  The left-hand term of our interval is 1 since it is the lower bound for our set, and there is a parenthesis around it since it is not in our set (1 is not greater than 1).  The right-hand term of our interval is 5 since it is the upper bound for our set, and there is a bracket around it since it is in our set (5 is less than or equal to 5).  Remember when dividing or multiplying an inequality by a negative number to switch the direction of the inequalities.

Example Question #66 : Solving Equations And Inequallities

Express the following linear inequality in interval notation.

\(\displaystyle -3< 1-2x\leq3\)

Possible Answers:

\(\displaystyle (3,6]\)

\(\displaystyle (-2,4]\)

\(\displaystyle (-2,4)\)

\(\displaystyle [-1,2)\)

\(\displaystyle (-1,2]\)

Correct answer:

\(\displaystyle [-1,2)\)

Explanation:

Upon solving for x, we find that -1 is less than or equal to x which is less than 2, or x is greater than or equal to -1 AND x is less than 2.  The left-hand term of our interval is -1 since it is the lower bound for our set, and there is a bracket around it since it is in our set (-1 is greater than or equal to -1).  The right-hand term of our interval is 2 since it is the upper bound for our set, and there is a parenthesis around it since it is not in our set (2 is not less than 2).  Remember when dividing or multiplying an inequality by a negative number to switch the direction of the inequalities.

Example Question #67 : Solving Equations And Inequallities

Express the following linear inequality in interval notation.

\(\displaystyle 3x\leq-6\)   or   \(\displaystyle x-1>0\)

Possible Answers:

\(\displaystyle (-\infty ,-2]\cup (1,\infty )\)

\(\displaystyle (-\infty ,-1]\cup (2,\infty )\)

\(\displaystyle (-\infty ,-1)\cup [2,\infty )\)

\(\displaystyle (-\infty ,-2)\cup [1,\infty )\)

\(\displaystyle (-\infty ,-3]\cup (6,\infty )\)

Correct answer:

\(\displaystyle (-\infty ,-2]\cup (1,\infty )\)

Explanation:

Upon solving for x, we find that x is less than or equal to -2 OR x is greater than 1. Since x may be in either of those sets, we must take the union of the sets.  The first interval begins with negative infinity, since x can be anything less than -2.  The first interval ends at -2 and includes it in the set, so there is a bracket around it.  We join this interval with the second interval beginning with 1, and there is a parenthesis around 1 since it is not in the set.  The second interval ends with infinity since any number larger than 1 is in our set. There are always parenthesis around infinities.

Example Question #68 : Solving Equations And Inequallities

Express the following linear inequality in interval notation.

\(\displaystyle 2x+3\leq-4\)  or  \(\displaystyle 2x+3\geq4\)

Possible Answers:

\(\displaystyle (-\infty ,-\frac{7}{2}]\cup[\frac{1}{2},\infty)\)

\(\displaystyle (-\infty ,-\frac{3}{2}]\cup[\frac{5}{2},\infty)\)

\(\displaystyle (-\infty ,-6]\cup[2,\infty)\)

\(\displaystyle (-\infty ,-\frac{5}{2}]\cup[\frac{3}{2},\infty)\)

\(\displaystyle (-\infty ,-\frac{1}{2}]\cup[\frac{7}{2},\infty)\)

Correct answer:

\(\displaystyle (-\infty ,-\frac{7}{2}]\cup[\frac{1}{2},\infty)\)

Explanation:

Upon solving for x, we find that x is less than or equal to -7/2 OR x is greater than or equal to 1/2. Since x may be in either of those sets, we must take the union of the sets.  The first interval begins with negative infinity, since x can be anything less than -7/2.  The first interval ends at -7/2 and includes it in the set, so there is a bracket around it.  We join this interval with the second interval beginning with 1/2, and there is a bracket around 1/2 since it is in the set.  The second interval ends with infinity since any number larger than 1/2 is in our set. There are always parenthesis around infinities.

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