Example

Try It: Solving 1x2+2x8>0\frac{1}{x^2 + 2x - 8} > 0

To solve the rational inequality 1x2+2x8>0\frac{1}{x^2 + 2x - 8} > 0, first factor the denominator to express the inequality as 1(x+4)(x2)>0\frac{1}{(x + 4)(x - 2)} > 0. Next, find the zero partition numbers. The quotient is zero when the numerator is zero; but since the numerator is the constant 11, this never occurs. The quotient is undefined when the denominator is zero, which happens when (x+4)(x2)=0(x + 4)(x - 2) = 0, resulting in x=4x = -4 and x=2x = 2. Use these zero partition numbers to divide the number line into three intervals: (,4)(-\infty, -4), (4,2)(-4, 2), and (2,)(2, \infty). Testing a value in each interval reveals that the quotient is positive for (,4)(-\infty, -4) and (2,)(2, \infty). Since the inequality specifies greater than 00, the zero partition numbers are not included. In interval notation, the solution is (,4)(2,)(-\infty, -4) \cup (2, \infty).

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Updated 2026-05-25

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