Do you mean just write it? Or is it equal to something. If it is equal to something, edit what you want or use a comment and I'll come back and do something with it.
3*sqrt(a) is one way to write it.
It could also be shown like this [tex]{3} \sqrt{a} [/tex]
It can be written as [tex] 3*a^{ \frac{1}{2} } [/tex] <<<< answer
[tex] \text{(9a)}^ \frac{1}{2} [/tex] <<<< alternate answer.
