WAEC 2022 · Paper 1 · Q31

Find the range of values of $x$ for which $2x^2 + 7x - 15 \ge 0$ .

Worked solution (try it first)

Factorise: $2x^2 + 7x - 15 = (2x - 3)(x + 5)$ , which is zero at $x = \frac32$ and $x = -5$ .
The $x^2$ coefficient is positive, so the curve is U-shaped and is above zero outside the roots.
So $x \le -5$ or $x \ge \frac32$ , option B.