Algebra · real student question

Solve the inequality (3x + 4)/4 > 2x - 4.

Question

Solve the inequality

3x+44>2x4\frac{3x+4}{4}>2x-4

Step-by-step solution

  1. Clear the denominator. Multiply both sides by 44. Since 4>04>0, the direction is preserved — and every term on the right must be multiplied, not just the first:

    3x+4>4(2x4)=8x163x+4>4(2x-4)=8x-16

  2. Choose which side to collect on. Subtracting 3x3x (the smaller coefficient) leaves a positive 5x5x on the right, so no sign flip will be needed later:

    4>5x164>5x-16

    Subtracting 8x8x instead would give 5x-5x and force a flip — the same answer, but with an extra chance to slip.

  3. Move the constant. Add 1616 to both sides:

    20>5x20>5x

  4. Divide by 5. Positive divisor, so the direction holds:

    4>x4>x

  5. Rewrite in conventional order. "44 is greater than xx" is the same as

    x<4x<4

    Flipping the reading of the statement is not the same as flipping the inequality — the variable simply moves to the left.

  6. Verify the boundary and both sides. At x=4x=4: left =164=4=\tfrac{16}{4}=4, right =84=4=8-4=4 — equal, so the strict inequality excludes it ✓. At x=0x=0 (inside): 1>41>-4 ✓. At x=6x=6 (outside): 224=5.5\tfrac{22}{4}=5.5 against 88, and 5.5>85.5>8 is false ✓. A scan of 40014001 exact rational points confirms the set is (,4)(-\infty,4) ✓.

Answer

x<4,(,4)x<4,\qquad(-\infty,4)

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