Find the magnetic induction of the field at the point OOO of a loop with current III, whose shape is illustrated (a) in Fig. 3.60a3.60 a3.60a, the radii aaa and bbb, as well as the angle φ\varphiφ are known; (b) in Fig. 3.60b3.60 b3.60b, the radius aaa and the side bbb are known.