Algebra · real student question

Solve the inequality -(1/3)(x - 7) >= (1/2)(3x + 1).

Question

Solve the inequality

13(x7)12(3x+1)-\frac13(x-7)\ge\frac12(3x+1)

Step-by-step solution

  1. Clear both denominators in one move. The denominators are 33 and 22, so multiply every term by their LCM 66. Because 6>06>0, the inequality direction is unaffected — this is the safe way to remove fractions:

    6[13(x7)]6[12(3x+1)]6\cdot\left[-\frac13(x-7)\right]\ge6\cdot\left[\frac12(3x+1)\right]

    2(x7)3(3x+1)-2(x-7)\ge3(3x+1)

  2. Distribute on both sides.

    2x+149x+3-2x+14\ge9x+3

    The 2-2 multiplies both terms inside the bracket, turning 7-7 into +14+14.

  3. Collect the variable on one side. Subtract 9x9x from both sides (adding or subtracting never flips the sign):

    11x+143-11x+14\ge3

    then subtract 1414:

    11x11-11x\ge-11

  4. Divide by the negative coefficient and flip. Dividing both sides by 11-11 reverses the inequality:

    x1x\le1

    This single sign reversal is the entire trap in the problem; keeping \ge here would give the exactly wrong half-line.

  5. Test one point on each side of the boundary. At x=1x=1: left =13(6)=2=-\tfrac13(-6)=2, right =12(4)=2=\tfrac12(4)=2, so equality holds ✓ (the endpoint is included). At x=0x=0: left =732.33=\tfrac73\approx2.33, right =0.5=0.5, and 2.330.52.33\ge0.5 is true ✓. At x=2x=2: left =531.67=-\tfrac53\approx-1.67, right =3.5=3.5, and 1.673.5-1.67\ge3.5 is false ✓. The solution set is (,1](-\infty,1].

Answer

x1or, in interval notation,(,1]x\le1\quad\text{or, in interval notation,}\quad(-\infty,\,1]

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