Quadratic inequalities

A quadratic inequality asks where a parabola is above or below zero, so the answer is a set of intervals.

• Move everything to one side, factorise, and find the critical values (roots).
• Sketch a rough parabola to see where it lies above or below the axis.
• ">" means where the sketch is ABOVE the x-axis; "<" means below.
• Write the answer with correct interval notation and "or" between separate intervals.

• Critical value — a root that separates the intervals.