(a) Equations $6.4 \mathrm{a}$ and $6.4 \mathrm{b}$ are expressions for normal $\left(\sigma^{\prime}\right)$ and shear $\left(\tau^{\prime}\right)$ stresses, respectively, as a function of the applied tensile stress $(\sigma)$ and the inclination angle of the plane on which these stresses are taken $(\theta \text { of Figure } 6.4) .$ Make a plot on which is presented the orientation parameters of these expressions (i.e., $\left.\cos ^{2} \theta \text { and } \sin \theta \cos \theta\right)$ versus $\theta$.
(b) From this plot, at what angle of inclination is the normal stress a maximum?
(c) Also, at what inclination angle is the shear stress a maximum?