Example

Example: Solving a Rational Inequality Using Interval Notation

To solve the rational inequality x−1x+3≥0\frac{x-1}{x+3} \ge 0, first identify the zero partition numbers where the numerator or denominator equals zero. The numerator x−1=0x-1 = 0 when x=1x=1, and the denominator x+3=0x+3 = 0 when x=−3x=-3. These zero partition numbers, 11 and −3-3, divide the number line into three intervals: (−∞,−3)(-\infty, -3), (−3,1)(-3, 1), and (1, infty). Testing a value in each interval—such as −4-4, 00, and 22—reveals the sign of the quotient. The quotient is positive in (−∞,−3)(-\infty, -3) and (1, infty), and negative in (−3,1)(-3, 1). Because the inequality requires the expression to be greater than or equal to zero, the intervals (−∞,−3)(-\infty, -3) and (1, infty) are solutions. The partition number x=−3x=-3 must be excluded with a parenthesis because it makes the denominator zero, yielding an undefined expression. The partition number x=1x=1 is included with a bracket because it makes the rational expression zero, which satisfies the ≥\ge condition. Connecting the two valid intervals with the union symbol gives the final solution: (−∞,−3)∪[1,∞)(-\infty, -3) \cup [1, \infty).

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Updated 2026-06-05

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