JAMB 2016 · UTME · Q13

If $y = x^2 - x - 12$ , find the range of values of $x$ for which $y \ge 0$ .

Worked solution (try it first)

Factorise: $x^2 - x - 12 = (x - 4)(x + 3)$ , so the roots are $x = 4$ and $x = -3$ .
The graph is a U shape, so $y \ge 0$ outside the roots and at the roots themselves.
So $x \le -3$ or $x \ge 4$ , option B.