Question 610641
Your question is not clear.
Maybe you meant a fourth root, and wanted to know how to write {{{root(4,18)}}} as a power with a rational exponent.
In that case,  {{{root(4,18)=18^(1/4)}}} , with a {{{1/4}}} as the exponent.
If it really was a square root, maybe the problem was {{{(sqrt(18))^4}}}
{{{(sqrt(18))^4=(sqrt(18))^((2*2))=((sqrt(18))^2)2=18^2=324}}}
You could solve that using rational exponents too, as in
{{{(sqrt(18))^4=(18^(1/2))^4=18^(((1/2)*4))=18^2=324}}}