Question 310971
I think you're getting confused on the symbols. 
It's not the square root, it's the cube root. 
I think that's what you mean by index 3 square root. 
Just like square root is to the ({{{1/2}}}) power, cube root is to the ({{{1/3}}}) power. 
You can pull the {{{8}}} out because {{{2^3=8}}} so the cube root of {{{8}}} is {{{2}}}.
You have no other factors in {{{20}}} that are cube roots so it's as simplified as it can be.
{{{(160)^(1/3)=(8*20)^(1/3)=8^(1/3)*20^(1/3)=2*(20)^(1/3)}}}