let's do the same here.
[tex]\bf -\cfrac{1}{\sqrt{18x}}\cdot \cfrac{\sqrt{18x}}{\sqrt{18x}}\implies -\cfrac{\sqrt{18x}}{\sqrt{(18x)^2}}\implies -\cfrac{\sqrt{18x}}{18x}\implies -\cfrac{\sqrt{9\cdot 2\cdot x}}{18x}
\\\\\\
-\cfrac{\sqrt{3^2\cdot 2\cdot x}}{18x}\implies -\cfrac{3\sqrt{ 2\cdot x}}{18x}\implies -\cfrac{\sqrt{2x}}{6x}[/tex]
