Jambmaths question:
If x – 3 is directly proportional to the square of y and x = 5 when y = 2, find x when y = 6
Option A:
30
Option B:
21
Option C:
16
Option D:
12
Jamb Maths Solution:
$\begin{align} & (x-3)\propto {{y}^{2}} \\ & x-3=k{{y}^{2}} \\ & \text{when }y=2,x=5 \\ & 5-3=4k \\ & k=\frac{1}{2} \\ & \text{when }y=6 \\ & x-3=\tfrac{1}{2}{{(6)}^{2}} \\ & x-3=18 \\ & x=21 \\\end{align}$
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