What is the relation between azimuth angle of the sun the bearing of an vertical object's shadow?
For example if the bearing of the shadow is 75° can we conclude that azimuth angle of the sun is 195°? Is the diagram below correct?
Your diagram is correct, your maths isn't.
The bearing of the object's shadow is, as your diagram shows, away from the sun. If the bearing of the shadow is 75°, then the sun must have an azimuth of of 75°+180°, or 255°.
Similarly if the bearing of the shadow was 300° (pointing towards the northwest) the sun would be at an azimuth of 300 - 180°, or 120° (in the southeast)