Is writing a 3 before a square root symbol the same as writing it after a square root symbol?

This depends as to whether you are just multiplying the square root by 3, or are doing a cube root function. In a cube root, the 3 would be located just at the bent part of the square root symbol, usually in a smaller font. If one just wanted to multiply a square root by 3, it does not matter whether or not the 3 comes before or after the root. 

A cube root is equal to a value to the power of (1/3).

I hope this helps