Let us first factorize #729# in to rime factors. As sum of digits of #729# is #18#, it is divisible by #9# i.e. we can divide it twice by #3#. Therefore
#729=3xx3xx81#
Again #81# is #9^2#, hence divisible bt #3# four times more. Hence,
#729=3xx3xx3xx3xx3xx3xx3#
and #root(3)729=root(3)(ul(3xx3xx3)xxul(3xx3xx3))#