Show that

$\frac{del{I}_{r^{\text{'}}}}{del{T}_{pq}}=T_{pq}^{\text{'}}$

where $I_T\text{'}$ is the second invariant of the deviatoric stress $T^{\text{'}}.($Warning: The de$-$

rivative is with respect to $T_{pq},$ not $T_{pq}^{\text{'}}.)$Show steps