Power / Root function issue

I'm having trouble finding the answer for this, or really any Nth root problem. Here is the particular problem that I cannot figure out. A simple explanation of how to solve this would go a long way, thank you.

Evaluate the function $\sqrt[5]{-243}$.

-
You are looking for the number $a$ with the property that $a^5 = -243$. Can you think of a number whose fifth power is $243$? – Arturo Magidin Mar 26 '12 at 3:43
Oh my god that's it? Thank you! Edit: 3 – stytown Mar 26 '12 at 3:45
Except $3$ doesn't work, because $3^5 = 243$ and you want the answer to be $-243$; so you'll need to do something to that $3$ to make sure you get $-243$ instead... – Arturo Magidin Mar 26 '12 at 3:46
-3 =) Thank you Arturo – stytown Mar 26 '12 at 3:51
For what it's worth, $\root5\of{-243}$ is not a function; it's a number. One key to success in Mathematics is understanding the vocabulary, and using it correctly. – Gerry Myerson Mar 26 '12 at 5:24

You are looking for the number $a$ with the property that $a^5=−243$. Can you think of a number whose fifth power is 243? – Arturo Magidin Mar 26 at 3:43
Except $3$ doesn't work, because $3^5=243$ and you want the answer to be $−243$; so you'll need to do something to that $3$ to make sure you get $−243$ instead... – Arturo Magidin Mar 26 at 3:46