Concept

Boundary Lines for Single-Variable Inequalities on the Coordinate Plane

Some linear inequalities involve only one variable — they contain xx but not yy, or yy but not xx. When such an inequality is graphed on the coordinate plane rather than on a number line, the boundary line takes a special form:

  • x=ax = a produces a vertical boundary line passing through every point whose x-coordinate is aa.
  • y=by = b produces a horizontal boundary line passing through every point whose y-coordinate is bb.

Once the boundary line is drawn (solid or dashed, depending on whether the inequality includes the equal sign), the same test-point-and-shade procedure used for two-variable inequalities determines which side of the line to shade.

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Updated 2026-05-03

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