Vector2Dot.cs

using UnityEngine;

public class VectorOperations : MonoBehaviour
{
    [SerializeField] private Vector3 _playerPosition = new Vector2(3, 1);
    [SerializeField] private Vector3 _guardPosition = new Vector2(1, 2);

    private float _dotResult;
    private Vector3 _fieldOfView = new Vector2(1, 1);

    private void Start()
    {
        _dotResult = Vector2.Dot(_fieldOfView, (_playerPosition - _guardPosition));
        Debug.Log(_dotResult); // Выведет 1, значит угол острый
    }
}