Algebra · real student question

Solve the inequality |2x - 1| <= 3.

Question

Solve

2x13|2x-1|\le3

Step-by-step solution

  1. Translate Ab|A|\le b into a single chain. The absolute value measures distance from 00, so requiring it to be at most 33 confines 2x12x-1 to the closed band between 3-3 and 33:

    32x13-3\le2x-1\le3

    Because the relation is at most (not at least), the result is one bounded interval rather than two rays — the direction of the inequality decides the shape of the answer.

  2. Add 1 to all three parts. Adding a constant everywhere leaves both directions intact:

    3+12x3+122x4-3+1\le2x\le3+1\qquad\Longrightarrow\qquad-2\le2x\le4

  3. Divide all three parts by 2. The divisor is positive, so no sign flips:

    1x2-1\le x\le2

  4. Write the answer as a closed interval.

    [1,2][-1,2]

    Both endpoints are included because the original allowed equality — the square brackets record exactly that.

  5. Verify the endpoints and the outside. At x=1x=-1: 2(1)1=3=33|2(-1)-1|=|-3|=3\le3 ✓. At x=2x=2: 41=33|4-1|=3\le3 ✓. At the centre x=12x=\tfrac12: 0=0|0|=0 ✓. Just outside, x=3x=3 gives 5=5|5|=5 ✗. Comparing the raw inequality with [1,2][-1,2] at 9090 exact rational points agrees everywhere ✓. Note the interval is centred on x=12x=\tfrac12, the point where 2x1=02x-1=0, with radius 32\tfrac32.

Answer

1x2-1\le x\le2

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