Solve
Divide both sides by and reverse the direction. The coefficient is negative, so dividing by it flips into :
The flip is not optional. Forgetting it yields , which is the complement of the true answer — wrong for every value of that matters.
Reduce the fraction. Both and are divisible by :
so the boundary is .
State the solution set.
The endpoint is excluded because the original inequality is strict.
Verify around the boundary. At : , and ✓ (inside). At : , and is false — endpoint correctly open ✓. At : ✗ (outside). The raw inequality and agree at exact rational points ✓.
Note the alternative that avoids the flip. Adding to both sides and subtracting gives , i.e. and ✓ — 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.
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