Note that :
1^3 - (3√3)^3 = ( 1 - 3√3) ( 1 + 3√3 + (3√3)^2 ) = ( 1 - 3√3) ( 1 + 3√3 + 3√9 ) = ( 1 - 3)
So
23√9
_______________ multiply top/bottom by ( 1 - 3√3)
( 1 + 3√3 + 3√9 )
23√9 ( 1 - 3√3)
____________________________ =
( 1 - 3√3) ( 1 + 3√3 + (3√3)^2 )
23√9 - 23√27
_____________ =
1 - 3
23√27 - 23√9
____________ =
3 - 1
2 * 3 - 23√9
__________ =
2
2 ( 3 - 3√9 )
___________ =
2
3 - 3√9 =
3 - 32/3