Find all principal stresses, the unit normal vectors in all principal directions, the maximum shear stress and the unit normal vector to the plane on which it acts. draw the three-dimensional mohr’s circle, labeling all key values. show all work, just using a calculator is not allowed. (a) σxx = 120, σyy = 60, σzz = −40, σxy = −30, σyz = 100, σxz = 50, (all in mpa). (b) σxx = σyy = σzz = 0, σxy = σyz = σxz = −50 mpa. (c) σxx = σyy = −20 mpa, σzz = 40 mpa, σxy = σyz = σxz = 0.