[tex]\bf \cfrac{-7x^2}{\sqrt{6x-6}}\cdot \cfrac{\sqrt{6x-6}}{\sqrt{6x-6}}\implies \cfrac{-7x^2\sqrt{6x-6}}{\sqrt{(6x-6)^2}}\implies \cfrac{-7x^2\sqrt{6x-6}}{6x-6}[/tex]
the idea being, getting rid of the pesky radical at the bottom, simply multiply it by something that'd raise it to the root, so it gets out :)
