Question

divide 18 under root 21 by 6 under root 7

Answer 1

$$\begin{gathered} \frac{18\sqrt{21}}{6\sqrt{7}} \\ =\frac{3\sqrt{21}}{\sqrt{7}} \\ =\frac{3\sqrt{21}}{\sqrt{7}}\times \frac{\sqrt{7}}{\sqrt{7}}\left[\mathrm{Rationalising}\mathrm{the}\mathrm{denominator}\right] \\ =\frac{3\sqrt{21\times 7}}{7} \\ =\frac{3\sqrt{7\times 7\times 3}}{7} \\ =\frac{3\times 7\sqrt{3}}{7} \\ =3\sqrt{3} \end{gathered}$$