An inequality is solved like an equation — find where the expression is zero — and then a sign test on each interval between those critical points decides which intervals belong to the answer. The shaded region in the graph is the solution set.
Worked example: x^2 - 4 > 0
Step by step
- x^{2} - 4 > 0
Start from the inequality.
- x^{2} - 4 > 0
Move everything to the left so we compare against 0.
- x = -2, x = 2
Find the critical points — where the expression equals 0 (or is undefined). They split the number line into test intervals.
- (-\infty,\, -2): +\;\;(-2,\, 2): -\;\;(2,\, \infty): +
Test a point inside each interval to find the sign of the expression there.
- \left(-\infty, -2\right) \cup \left(2, \infty\right)
Keep the intervals whose sign satisfies the inequality (closed endpoints for ≤ / ≥, open for < / >).
- \left(-\infty < x \wedge x < -2\right) \vee \left(2 < x \wedge x < \infty\right)
The same answer written as inequalities.
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