Go Exercise: Loops and Functions - http://tour.golang.org/flowcontrol/8

sqrt.go

package main

import (
	"fmt"
	"math"
)

func Sqrt(x float64) float64 {
	z, delta := 1.0, 0.0000001
	for i :=0; i <= 100; i++ { // limit iterations to 100
		if value := z - (z * z - x) / (2 * z); math.Abs(value - z) < delta {
			// Delta reached, return value
			return value
		} else {
			// Continue assigning
			z = value
			// Show iterations done
			fmt.Println(z)
		}
	}
	// Loop ended, return value
	return z
}

func main() {
	fmt.Println(Sqrt(10), math.Sqrt(10))
}

Now handles errors

https://gist.github.com/evandertino/4129baab2b02200137c0#file-sqrt_err-go