Algebra · real student question

Solve the inequality x - 1/3 > x + 4.

Question

Solve

x13>x+4x-\frac{1}{3}>x+4

Step-by-step solution

  1. Collect the variable terms as usual. Both sides carry exactly one xx with coefficient 11, so subtract xx from both sides:

    x13x>x+4xx-\frac{1}{3}-x>x+4-x

  2. Notice the variable disappears completely. The xx terms cancel on both sides, leaving a statement with no variable in it at all:

    13>4-\frac{1}{3}>4

    This is not a dead end — it is the answer in disguise. When the variable vanishes, the surviving numeric claim decides the whole problem at once.

  3. Judge the surviving statement. Is 13-\tfrac13 greater than 44? No: 130.333-\tfrac13\approx-0.333 is negative while 44 is positive, so the claim is false. Since it does not depend on xx, it is false for every xx simultaneously.

  4. Conclude with the empty set. No real number satisfies the inequality, so

    solution set=\text{solution set}=\varnothing

    Testing 200200 exact rational values of xx produced no solution ✓ — as expected, since the two sides differ by a constant.

  5. See why geometrically. The lines y=x13y=x-\tfrac13 and y=x+4y=x+4 have the same slope 11, so they are parallel and never cross. The left line sits a constant 4+13=1334+\tfrac13=\tfrac{13}{3} below the right one, so it can never be above it. Had the inequality been reversed, x13<x+4x-\tfrac13<x+4, the leftover statement 13<4-\tfrac13<4 would be true and the solution set would be all real numbers.

Answer

 (no solution)\varnothing\ \text{(no solution)}

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