Write the solution of the absolute value inequality the absolute value of (x - 7) less than or equal to 3.
AThe interval [-10, -4]
BThe interval [4, 10]
CThe interval [3, 11]
DThe interval [7, 10]
Answer & Solution
Correct answer: B. The interval [4, 10]
1. An absolute value at most 3 means the distance from the inside expression to zero is at most 3.
2. So the inside expression lies between negative 3 and 3 inclusive.
3. Write that as negative 3 less than or equal to x minus 7, which is less than or equal to 3.
4. Add 7 to all three parts to isolate x.
5. The left end becomes negative 3 plus 7, which is 4.
6. The right end becomes 3 plus 7, which is 10.
7. Both signs allow equality, so both endpoints are included and take brackets.
8. The solution is therefore the closed interval from 4 to 10.
9. The interval [3, 11] adds and subtracts around the wrong centre.
10. The interval [7, 10] keeps only the half of the solution above the centre.
_Source: OpenStax College Algebra (CC BY 4.0), section 2.7 Linear Inequalities and Absolute Value Inequalities_
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