A rectangular beam section is subjected to arial force $N,$ and bending moments in two directions: $M_y$ in the $xy$ plane and $M_z$ in the $xz$ plane. The principal anes $YZ$ are shown, in which the angle between $Y-$axis and $y-$axis is $.$ Calculate

a$)$ normalstresses at four corners of section, point $A,B,D,E$

b$)$ equation of neutral anis colution$)$ are in terms of $N,M_y,M_z,b,$

YZ:principal anes

xy plane