A Go implementation of Newton's method for finding the square root of a number.

sqrt.go

package main

import (
	"fmt"
	"math"
)

func Sqrt(x float64) float64 {
	return SqrtNewton(x, x)
}

func SqrtNewton(x float64, z float64) float64 {
	nextz := z - (z*z-x)/(2*z)
	if math.Abs(z-nextz) < 0.001 {
		return nextz
	}
	return SqrtNewton(x, nextz)
}

func main() {
	fmt.Println(Sqrt(2))
}