waecmaths question:
Find the value of y for which the expression $\frac{{{y}^{2}}-9y+18}{{{y}^{2}}+4y-21}$is undefined.
Option A:
6, –7
Option B:
3, – 6
Option C:
3, –7
Option D:
–3, –7
waecmaths solution:
$\begin{align} & \text{For the expression}\frac{{{y}^{2}}-9y+18}{{{y}^{2}}+4y-21}\text{ to undefined }{{y}^{2}}+4y-21=0 \\ & {{y}^{2}}+4y-21=0 \\ & (y+7)(y-3)=0 \\ & y=-7,\text{ }y=3 \\\end{align}$
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