Chapter R - Algebra Reference - R.5 Inequalities - R.5 Exercises - Page R-21: 33

$x^2-4x \geq 5$ $x^2-4x-5\geq0$ $(x+1)(x-5)\geq0$ $x\leq-1$ and $x\geq5$

Step 1: Subtract 5 from both sides of the inequality Step 2: Factorize Inequality (trinomial) Step 3: The quadratic inequality is greater and equal to $0$ for $x\leq-1$ and $x\geq5$