Then you can use Surd
, as Henrik suggested
Surd[7 + Sqrt[50], 5] + Surd[7 - Sqrt[50], 5] // N
CubeRoot
is just a special form of Surd
. The following will give the same result as if CubeRoot
was used, in case of power 1/3:
Surd[7 + Sqrt[50], 3] + Surd[7 - Sqrt[50], 3] // N