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Algebra · real student question

Solve the inequality -6x > 8.

Question

Solve

−6x>8-6x>8

Step-by-step solution

  1. Divide both sides by −6-6 and reverse the direction. The coefficient is negative, so dividing by it flips >> into <<:

    −6x−6<8−6⟹x<−86\frac{-6x}{-6}<\frac{8}{-6}\qquad\Longrightarrow\qquad x<-\frac{8}{6}

    The flip is not optional. Forgetting it yields x>−43x>-\tfrac43, which is the complement of the true answer — wrong for every value of xx that matters.

  2. Reduce the fraction. Both 88 and 66 are divisible by 22:

    −86=−43-\frac{8}{6}=-\frac{4}{3}

    so the boundary is −43≈−1.333-\tfrac43\approx-1.333.

  3. State the solution set.

    x<−43,i.e.(−∞,−43)x<-\frac{4}{3},\qquad\text{i.e.}\qquad\left(-\infty,-\tfrac{4}{3}\right)

    The endpoint is excluded because the original inequality is strict.

  4. Verify around the boundary. At x=−2x=-2: −6(−2)=12-6(-2)=12, and 12>812>8 ✓ (inside). At x=−43x=-\tfrac43: −6(−43)=8-6\left(-\tfrac43\right)=8, and 8>88>8 is false — endpoint correctly open ✓. At x=0x=0: 0>80>8 ✗ (outside). The raw inequality and x<−43x<-\tfrac43 agree at 5050 exact rational points ✓.

  5. Note the alternative that avoids the flip. Adding 6x6x to both sides and subtracting 88 gives −8>6x-8>6x, i.e. 6x<−86x<-8 and x<−43x<-\tfrac43 ✓ — the same answer using only a positive divisor. Rearranging so the variable's coefficient is positive is a reliable way to avoid the sign-flip trap altogether.

Answer

x<−43x<-\frac{4}{3}

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