My GoTour Exercise #48 (http://tour.golang.org/#48) solution

gistfile1.go

package main

import (
  "fmt"
  "math"
  "math/cmplx"
)

func cbrt(target, guess complex128) complex128 {
	return guess - (cmplx.Pow(guess, 3)-target)/(3*cmplx.Pow(guess,2))
}

func inequiv(a, b complex128) bool {
//This is probably cheating
	return math.Nextafter(real(a), real(b)) != real(b)
}

func Cbrt(x complex128) complex128 {
	curr, guess := complex128(0), complex128(10)
	for inequiv(curr, guess) {
                curr = cbrt(x, guess)
		guess = (curr + guess) / 2
	}
	return guess
}

func main() {
	fmt.Println(Cbrt(2))
	fmt.Println(math.Cbrt(2))
}