$7\mathrm{.}9$ through $7\mathrm{.}12$ For the given state of stress, determine $(a)$ the orientation of the planes of maximum in$-$plane shearing stress, $($b$)$ the

maximum in$-$plane shearing stress, $($c$)$ the corresponding normal stress.

Fig. P$7\mathrm{.}5$ and P$7\mathrm{.}9$

Fig. P$7\mathrm{.}6$ and P$7\mathrm{.}10$