Unexpected <type> at the end of statement

Variable declaration in Go

static var var_name data_type = value

or

dynamic: var_name := value

In your case at line 9 you have missed both standard

Change line 9 to either of statements below:

v := math.Pow(x,n) // implicit type declaration and assignment

or

var v float64 = math.Pow(x,n) // explicit type declaration and assignment

See short variable declarations.