2. $\displaystyle -\frac{3}{\sqrt{18}} = -\frac{3}{\sqrt{9\times 2}} = -\frac{3}{\sqrt{9}\sqrt{2}} = -\frac{3}{3\sqrt{2}} = -\frac{1}{\sqrt{2}}.$
3. $-3/sqrt(18)=-3/sqrt(9*2)$
now what is $sqrt(a*b)$