En México se dice "equis cuadrada".
x cubed is an "equis al cubo"... sometimes (not too often) "equis cúbica"
Raise to a power is "elevar a la [cuarta, quinta, etc.] potencia"
As for the roots, it's the same as Irma has said.
By the way, Lou Ann, all the letters (and variables) in Spanish are always referred to in feminine.