P.1.2. At a point in an elastic material, there are two mutually perpendicular planes, one of which carries a direct tensile stress of 50 N/mm² and a shear stress of

40 N/mm2, while the other plane is subjected to a direct compressive stress of 35 N/mm and a complementary shear stress of40 N/mm?. Determine the principal stresses at the point, the position of the planes on which the act, and the position of the planes on which there is no normal stress. Answer:O1 = 65.9 N/mm²,0 = 21°38' O = -50.9 N/mm2, 0 = 111°38'