고체역학 (Beer) — Torsion: Problem 3.129

3.129 Two shafts are made of the same material. The cross section of shaft A is a square of side $b$ and that of shaft B is a circle of diameter $b$. Knowing that the shafts are subjected to the same torque, determine the ratio $\tau_A/\tau_B$ of maximum shearing stresses occurring in the shafts.