rotate by vector 3 unity code example

Example 1: unity 2d rotate towards direction

/// <summary>
    /// Rotate a gameobject to face a direction in 2D space with offet
    /// </summary>
    /// <param name="target"></param>
    /// <param name="RotationSpeed"></param>
    /// <param name="offset"></param>
    private void RotateGameObject(Vector3 target, float RotationSpeed, float offset)
    {
        //https://www.youtube.com/watch?v=mKLp-2iseDc
        //get the direction of the other object from current object
        Vector3 dir = target - transform.position;
        //get the angle from current direction facing to desired target
        float angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
        //set the angle into a quaternion + sprite offset depending on initial sprite facing direction
        Quaternion rotation = Quaternion.Euler(new Vector3(0, 0, angle + offset));
        //Roatate current game object to face the target using a slerp function which adds some smoothing to the move
        transform.rotation = Quaternion.Slerp(transform.rotation, rotation, RotationSpeed * Time.deltaTime);
    }

Example 2: rotate 2d vector by angle

rotate vector (x1, y1) counterclockwise by the given angle
(angle in radians)

newX = oldX * cos(angle) - oldY * sin(angle)
newY = oldX * sin(angle) + oldY * cos(angle)