Mathf.Sqrt

public static float Sqrt (float f);

Description

Возвращает квадратный корень из f.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    // The formula made famous by Pythagoras, also used internally by
    // Vector3.Distance and several other standard functions.
    float HypotenuseLength(float sideALength, float sideBLength)
    {
        return Mathf.Sqrt(sideALength * sideALength + sideBLength * sideBLength);
    }
}