Please see the attachment.
Bio-Savarat law is given as:
Where I is the current, dl is the vector path element along the wire and r is the vector from the dl to the point where we want to evaluate the field.
We immediately see that segments AD and BC do not contribute anything to the magnetic field at the center because
On the curved segments, the radius id always perpendicular to ...
This solution determines the magnetic field at point P two different steady current configurations.