NECO 2023 · Paper 1 · Q26

Solve the equation $2x + 8 = 21x^2$ .

Worked solution (try it first)

Bring everything to one side: $21x^2 - 2x - 8 = 0$ .
Find two numbers with product $21 \times (-8) = -168$ and sum $-2$ : they are $-14$ and 12.
Split and group: $21x^2 - 14x + 12x - 8 = 7x(3x - 2) + 4(3x - 2)$
$= (3x - 2)(7x + 4)$ .
So $x = \frac23$ or $x = -\frac47$ , option B.