How to find perpendicular line in 2D?

Found how to do it:

      var first = points[0];
                     var second = points[1];
                     var newVec = first-second;
                     var newVector = Vector3.Cross (newVec, Vector3.forward);
 newVector.Normalize();
 
                     var newPoint = width*newVector+first;
                     var newPoint2 = -width*newVector+first;
                     Debug.DrawLine (newPoint,newPoint2);

Thought I would share the C# approach that worked for me with some inspiration of these answers:

 Vector2 vNormalized = (P1.position - P2.position).normalized;
 Vector2 vPerpendicular = new Vector2(vNormalized.y, -vNormalized.x).normalized;
 Vector2 P4 = new Vector2(P1.position.x, P1.position.y) + (vPerpendicular * h);

I may have a redundant normalization but it is working great, and the idea is first get the vector from 1 to 2. Then make a new vector (y, -x) on this angle, switch to (-y, x) for P3.

Cheers,