Question 83429
It sounds like your problem is this, which is NOT a SQUARE root!  It is a CUBE root!
{{{ root(3,(-8/27)) }}}


This means the cube root of {{{-8/27}}}.  This means basically, "What number would you have to cube in order to end up with {{{-8/27}}}. Before you begin a cube root problem, you must know your perfect cubes: 
 {{{2^3=8}}}  
{{{3^3=27}}} 
{{{4^3=64}}} 
{{{5^3=125}}} 


It might be helpful to break this up and write it this way:
{{{ root(3,(-8/27)) }}}= {{{ root(3,(-8))/root(3,27) }}}
The numerator of the answer must be -2, and the denominator must be 3.  Therefore, the answer is {{{(-2)/3}}} or {{{-2/3}}}


R^2 at SCC