WAEC 2021 · Paper 1 · Q12

Simplify $2\sqrt7 - \dfrac{14}{\sqrt7} + \dfrac{7}{\sqrt{21}}$ .

Worked solution (try it first)

Rationalise: $\dfrac{14}{\sqrt7} = \dfrac{14\sqrt7}{7}$ , which is $2\sqrt7$ .
So the first two terms cancel.
Rationalise the last term: $\dfrac{7}{\sqrt{21}} = \dfrac{7\sqrt{21}}{21}$ , which is $\dfrac{\sqrt{21}}{3}$ .
So the value is $\dfrac{\sqrt{21}}{3}$ , option C.