P4) The pre-existing stress state in the ground is measured by some means and the results are of = 3200 psi, o, = 2100 psi o; = 1800 psi. These values are measured on three different planes, which are perpendicular to each other, and the normal axes orthogonal to these planes constitute the /mn coordinate system. A) Given the following angles to find out the direction cosines, calculate the stress matrix in xyz coordinate system