Solve the inequality
Distribute the -2 across the parentheses. The minus sign belongs to the , so both inner terms change: and . Dropping that sign flip on the second term is the classic mistake here.
Combine the constants on the left. , giving
Move the n terms to one side by adding 8n. Adding the same quantity to both sides never changes the direction of an inequality, and adding (rather than subtracting ) keeps the coefficient positive, which avoids a later flip:
Isolate the n term. Subtract from both sides:
Divide by 6 and explain why the sign holds. Because , dividing preserves :
The fraction does not reduce, since is prime and does not divide . As a decimal, .
Check the boundary and one interior point. At : left and right — equal, as expected at the boundary ✓. At (inside the solution set): ✓, so the inequality really does point the way stated.
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