You can put this solution on YOUR website! The radical symbol is used for all kinds of roots: square roots, cube roots, 4th roots, etc. So saying "radical 5" is not a correct way to describe whatever it is in your problem. (It is just incorrect to say "root 5".) Please tell us what kind of root it is. If it is a square root, then say "square root of 5" (or just "sqrt(5)".
And what is inside your radical? The 5? of the whole fraction, 5/3? Use parentheses to make things clear. For example sqrt(5)/3 if just the 5 is in the square root and sqrt(5/3) if the whole fraction should be inside the square root.
Please re-post your question in a clear enough way that we can figure out what the problem actually is.
P.S. Now that I know what the problem is...
What we are trying to do is figure out what cos(2A) is when all we have to start with is
There are three variations to the cos(2A) formula:
Fortunately, the last one only requires sin(A). So we will use that one:
(