Jambmaths question:
Make r the subject of the formula $\frac{x}{r+a}=\frac{a}{r}$
Option A:
$\frac{{{a}^{2}}}{x-a}$
Option B:
$\frac{{{a}^{2}}}{x+a}$
Option C:
$\frac{a}{x-a}$
Option D:
$\frac{a}{x+a}$
Jamb Maths Solution:
$\begin{align} & \frac{x}{r+a}=\frac{a}{r} \\ & rx=a(r+a)\text{ (cross multiply)} \\ & rx=ar+{{a}^{2}} \\ & rx-ar={{a}^{2}}\text{ (collect the like terms)} \\ & r(x-a)={{a}^{2}}\text{ (factorize }r\text{ out)} \\ & r=\frac{{{a}^{2}}}{x-a} \\\end{align}$
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