Expression denotes a `method group', where a `variable', `value' or `type' was expected

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class Truster : MonoBehaviour {


	void Update() {

		if (Input.GetKey (KeyCode.LeftControl)){
			GameObject.Find("sphere 2").GetComponent.AddRelativeForce(Vector3.down * 2);
		}

	}
}

Why do I get this error?
Expression denotes a method group', where a variable’, value' or type’ was expected

I think your call of GetComponent is wrong.

try like this :

GameObject.Find(“sphere 2”).GetComponent< RigidBody >().AddRelativeForce(Vector3.down * 2);