JAMB 2013 · UTME · Q17

Quadratics & their graphs

A curve crosses the $x$ -axis at $-1$ and $2$ and the $y$ -axis at $-2$ (see the graph). The graph is correctly represented by

Try it on a graph

The graph crosses the x-axis at −1 and 2 and the y-axis at −2.

Worked solution (try it first)

The curve crosses the $x$ -axis at $-1$ and 2, so $y = k(x + 1)(x - 2)$ .
It crosses the $y$ -axis at $-2$ : at $x = 0$ , $k(1)(-2) = -2$ , so $k = 1$ .
So $y = (x + 1)(x - 2) = x^2 - x - 2$ , option C.

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