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Absolute value inequalities

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5244899
A number \(x\) satisfies \(|x| < 2.5\) and \(x > -1\). Describe all possible values of \(x\) with a compound inequality of the form \(a < x < b\).

Hints

- Rewrite the absolute value inequality as a compound inequality. - Represent the second condition on the same number line. - Find the overlap of the two solution sets.

Solution

1. The condition \(|x| < 2.5\) is equivalent to \(-2.5 < x < 2.5\). 2. The second condition requires \(x > -1\). 3. The intersection of the two conditions is \(-1 < x < 2.5\).

Answer

\(-1 < x < 2.5\)
5244959
Find the solution set of \(|x - 2| \le 4\) over the rational numbers. Explain your result by interpreting absolute value as distance on the number line.

Hints

- Interpret \(|x - 2|\) as distance from \(2\). - Identify the points exactly \(4\) units from \(2\). - Because the inequality includes equality, include both endpoints. - Rewrite the condition as a compound inequality.

Solution

1. The expression \(|x - 2|\) is the distance from \(x\) to \(2\). 2. The condition says this distance is at most \(4\). 3. Rewrite the absolute value inequality as \(-4 \le x - 2 \le 4\). 4. Add \(2\) to all three parts: \(-2 \le x \le 6\). 5. Therefore, the solution set is every rational number in \([-2, 6]\).

Answer

\(S = \{x \in \mathbb{Q} \mid -2 \le x \le 6\}\)
5241029
Find all integers \(z\) that satisfy both conditions: 1. \(-3 < z < 5\) 2. \(|z| > 2\)

Hints

- List the integers satisfying the first condition. - Interpret absolute value as distance from \(0\). - Keep only values whose distance is strictly greater than \(2\).

Solution

1. The integers satisfying \(-3 < z < 5\) are \(-2, -1, 0, 1, 2, 3, 4\). 2. The condition \(|z| > 2\) means that the distance from \(0\) is greater than \(2\). 3. Among the listed integers, only \(3\) and \(4\) have absolute value greater than \(2\).

Answer

\(S = \{3, 4\}\)
5241049
Analyze each absolute value condition. a) Rewrite \(|x| < 7\) as a compound inequality without absolute value symbols. b) Write \(|x| \le 3.5\) in interval notation. c) Write an absolute value inequality whose solution set is \((-9.2, 9.2)\). d) Explain why \(|x| < -1\) has no solution.

Hints

- Interpret absolute value as distance from \(0\). - A distance less than a positive number creates a symmetric interval. - Decide whether each endpoint is included. - A distance cannot be negative.

Solution

1. The condition \(|x| < 7\) means that the distance from \(x\) to \(0\) is less than \(7\), so \(-7 < x < 7\). 2. The condition \(|x| \le 3.5\) means \(-3.5 \le x \le 3.5\), so the interval is \([-3.5, 3.5]\). 3. The symmetric open interval \((-9.2, 9.2)\) is represented by \(|x| < 9.2\). 4. Absolute value represents distance and is always nonnegative. It can never be less than \(-1\), so the solution set is empty.

Answer

a) \(-7 < x < 7\) b) \([-3.5, 3.5]\) c) \(|x| < 9.2\) d) No solution; \(|x|\) cannot be negative.
5244909
Two students discuss an unknown number \(z\). Ethan says, “The absolute value of \(z\) is at most \(6\).” Maya says, “The distance from \(z\) to \(4\) on the number line is at most \(3\).” Does every number that satisfies Maya's statement also satisfy Ethan's statement? Determine both solution sets and justify your answer.

Hints

- Rewrite each absolute value statement as an interval. - Interpret \(|z - 4|\) as distance from \(4\). - Compare the endpoints of the two intervals. - Look for a counterexample in Maya's interval but outside Ethan's.

Solution

1. Ethan's statement is \(|z| \le 6\), which is equivalent to \(-6 \le z \le 6\). 2. Maya's statement is \(|z - 4| \le 3\), which is equivalent to \(1 \le z \le 7\). 3. Maya's interval extends to \(7\), while Ethan's interval ends at \(6\). 4. The number \(7\) is a counterexample: it is \(3\) units from \(4\), but \(|7| = 7 > 6\). 5. Therefore, not every number satisfying Maya's statement satisfies Ethan's statement.

Answer

No. Maya''s solution set is \([1, 7]\), while Ethan''s is \([-6, 6]\). For example, \(z = 7\) satisfies Maya''s condition but not Ethan''s.
5244969
Find each solution set over the rational numbers. a) \(|2x + 6| < 10\) b) \(4|x - 1| - 5 \ge 7\)

Hints

- Isolate the absolute value expression first. - An inequality of the form \(|u| < a\) describes values between two boundaries. - An inequality of the form \(|u| \ge a\) describes two outer regions. - Solve both cases in part b).

Solution

1. For a), rewrite the inequality as \(-10 < 2x + 6 < 10\). 2. Subtract \(6\): \(-16 < 2x < 4\). Divide by \(2\): \(-8 < x < 2\). 3. For b), add \(5\): \(4|x - 1| \ge 12\). Divide by \(4\): \(|x - 1| \ge 3\). 4. A distance of at least \(3\) from \(1\) means \(x - 1 \ge 3\) or \(x - 1 \le -3\). 5. Solve the two cases: \(x \ge 4\) or \(x \le -2\).

Answer

a) \(S = \{x \in \mathbb{Q} \mid -8 < x < 2\}\) b) \(S = \{x \in \mathbb{Q} \mid x \le -2 \text{ or } x \ge 4\}\)

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