how to calculate rotation matrix 2d example

Example: get 2d rotation from 2 position math

Vector3 dir = new Vector3(position2.x - position1.x, position2.y - position1.y);
float angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
Quaternion rotation = Quaternion.Euler( 0f, 0f, angle );