Determine the maximum tensile stress σt(due to pure bending about a horizontal axis through C by positive bending moments M) for beams having cross sections as follows (see figure).
(a) A semicircle of diameter d
(b) An isosceles trapezoid with bases b1= b and b2= 4b/3, and altitude h.
(c) A circular sector with α = π/3 and r = d/2
