Multiplying or dividing by a negative number reverses the inequality sign because the operation reverses the order of values on the number line. If one quantity is greater than another before both are multiplied by a negative value, their resulting positions switch order. Reversing the symbol preserves the statement’s truth and prevents an incorrect solution set.
A comparison using > or < excludes equality, whereas ≥ or ≤ allows the two sides to be equal. This distinction changes the boundary of the solution set. It matters when a condition describes an exact limit, such as values that may reach a threshold, versus values that must remain strictly above or below it.
Adding or subtracting the same value from both sides keeps the inequality direction unchanged. These operations shift both quantities equally along the number line, so their order does not change. In a multi-step comparison, this rule lets a solver remove a constant term while maintaining an equivalent statement, provided the same operation is applied to both sides.
First simplify both sides, then use addition or subtraction to isolate the variable. If isolating it requires multiplication or division by a negative number, reverse the inequality sign at that step. The final statement identifies the allowed values, which can then be represented as a range or shown graphically.
Graphical representations show which values satisfy an inequality rather than a single equality. A solution is interpreted as a set or range of positions on the number line, extending toward values that remain greater or less than the boundary. The inequality symbol determines whether the boundary itself is included, so the graph must match the written condition.
In algebra and modeling, inequalities express constraints when a quantity need not equal one fixed value. They can describe allowable measurements, minimum or maximum conditions, or choices that meet a requirement. Comparing these ranges supports decisions based on limits rather than exact equality, while the resulting solution set shows all values consistent with the constraint.