$={?}_{?}=\left[\begin{array}{ccc}0\mathrm{.}1& 0\mathrm{.}6& 0\mathrm{.}0\\ 0\mathrm{.}6& 1\mathrm{.}2& 0\mathrm{.}0\\ 0\mathrm{.}0& 0\mathrm{.}0& 0\mathrm{.}3\end{array}\right]$MPa

$5+5=10$

$($a$)$ Find the traction vector on an element of

the plane $x_1+x_2+x_3=0$

$($b$)$ Find the normal stress and the shoor

stress on the said plane.