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WAEC Mathematics 2018 Paper

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Question : 3

Total: 50

Given that y varies inversely as the square of x. If x = 3 when y = 100, find the equation connecting x and y.

$yx^2 = 300$
$yx^2 = 900$
y = $\; \frac{100x}{9}$
$y = 900x^2$

Solution:

Y $\alpha \; \frac{1}{x^2} \rightarrow y = \; \frac{k}{x^2}$

If x = 3 and y = 100,

then, $\; \frac{100}{1} = \; \frac{k}{3^2}$

$\; \frac{100}{1} = \; \frac{k}{9}$

k = 100 x 9 = 900

Substitute 900 for k in

y = $\; \frac{k}{x^2}$ ; y = $\; \frac{900}{x^2}$

= $yx^2 = 900$

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