Algebra · real student question

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

Question

Solve

7w6217|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:

    w63|w-6|\ge 3

  2. Read the inequality as a distance statement. w6|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, Ab|A|\ge b becomes AbA\le -b or AbA\ge b:

    w63orw63w-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:

    w3orw9w\le 3\qquad\text{or}\qquad w\ge 9

  5. Confirm the endpoints belong. The inequality is non-strict, so test them: 736=21217|3-6|=21\ge 21 \checkmark and 796=21217|9-6|=21\ge 21 \checkmark. A midpoint check rules out the middle: 766=0≱217|6-6|=0\not\ge 21 \checkmark. The solution set is (,3][9,)(-\infty,3]\cup[9,\infty).

Answer

w3orw9,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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