WAEC 2020 · Paper 1 · Q23

Simplify $\dfrac ab - \dfrac ba - \dfrac cb$ .

Worked solution (try it first)

The LCD of $b$ , $a$ and $b$ is $ab$ .
Rewrite each fraction over $ab$ : $\frac{a^2}{ab} - \frac{b^2}{ab} - \frac{ac}{ab}$ .
So the expression is $\dfrac{a^2 - b^2 - ac}{ab}$ , option D.