Did you read the API on the Math class? It tells you quite clearly:
static double sqrt(double a)
Returns the correctly rounded positive square root of a double value.
so if you want the square root, you use this.
static double pow(double a, double b)
Returns the value of the first argument raised to the power of the second argument.
If you want to raise a number to some arbitrary power, you use this.
Since raising a number to the 1/2 power is BY DEFINITION taking the square root, you can use either one you want.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors