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Algebra · real student question

Solve the inequality 7|w - 6| >= 21.

Question

Solve

7∣w−6∣≥217|w-6|\ge 21

Step-by-step solution

  1. Divide by the positive coefficient. The bars must be alone before splitting, and dividing by 7>07>0 leaves the direction unchanged:

    ∣w−6∣≥3|w-6|\ge 3

  2. Read the inequality as a distance statement. ∣w−6∣|w-6| is the distance from ww to 66, so the inequality says: ww is at least 33 units away from 66. Walking 33 units left of 66 lands on 33; walking 33 units right lands on 99.

  3. Write the two branches formally. For b>0b>0, ∣A∣≥b|A|\ge b becomes A≤−bA\le -b or A≥bA\ge b:

    w−6≤−3orw−6≥3w-6\le -3\qquad\text{or}\qquad w-6\ge 3

  4. Add 66 to each branch. No sign flipping is needed because adding a constant never changes direction:

    w≤3orw≥9w\le 3\qquad\text{or}\qquad w\ge 9

  5. Confirm the endpoints belong. The inequality is non-strict, so test them: 7∣3−6∣=21≥217|3-6|=21\ge 21 ✓\checkmark and 7∣9−6∣=21≥217|9-6|=21\ge 21 ✓\checkmark. A midpoint check rules out the middle: 7∣6−6∣=0≱217|6-6|=0\not\ge 21 ✓\checkmark. The solution set is (−∞,3]∪[9,∞)(-\infty,3]\cup[9,\infty).

Answer

w≤3orw≥9,i.e. (−∞,3]∪[9,∞)w\le 3\quad\text{or}\quad w\ge 9,\qquad\text{i.e. }(-\infty,3]\cup[9,\infty)

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