求二次根式(by go)

// Sqrt returns an approximation to the square root of x.
func Sqrt(x float64) float64 {
        // This is a terrible implementation.
        // Real code should import "math" and use math.Sqrt.
        z := 0.0
        for i := 0; i < 1000; i++ {
                z -= (z*z - x) / (2 * x)
        }
        return z
}

Sqrt(2) = 1.414213562373095