The question I was working on was to rationalize the denominator of $$\frac{1}{\sqrt{3}(\sqrt{21}+\sqrt{7})}$$
My answer was $\frac{\sqrt7}{42}(3-\sqrt{3})$.
But both my book and Symbolab gave the answer as $\frac{1}{42}(3\sqrt{7}-\sqrt{21})$.
Why shouldn't I factor out the $\sqrt{7}$?
Thanks for your help.