Order rules for real inequalities
Scaling an inequality depends on the factor's sign.
Key knowledge
Adding the same real number to both sides preserves a strict inequality. Multiplying by a positive number preserves its direction; multiplying by a negative number reverses it. The corresponding rules hold for non-strict inequalities.
Values and equations
a<b ⇔ a+c<b+c; for t>0, a<b ⇔ ta<tb; for t<0, a<b ⇔ ta>tb
- a, b, c
- Real numbers
- t
- Nonzero real scaling factor
Conditions and scope
- To divide, the divisor must be nonzero and its sign must be known.
- Multiplication by zero loses the original comparison and is not a reversible solving step.
Order-preserving/reversing real operations; no unqualified division by unknown-sign expressions.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Checked the stated order rules for real inequalities and restrictions against the listed primary sections; exact inspected boundaries are in the author receipt.
2026-10-10 · Independent Physics and Measurement reference editor (AI editorial bounded review). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
Entry details
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- foundation-math-inequality-rules
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions