JAMB 1998 · UME · Q14

Make $\frac ax$ the subject of the formula $\dfrac{x + a}{x - a} = m$ .

Worked solution (try it first)

Divide the top and bottom of the left side by $x$ : $\dfrac{1 + \frac ax}{1 - \frac ax} = m$ .
Multiply out: $1 + \frac ax = m - m\frac ax$ , so $\frac ax(1 + m) = m - 1$ .
Divide by $1 + m$ : $\frac ax = \dfrac{m - 1}{m + 1}$ , option A.