Chapter 9, Problem 9.78P

The $\text{L}80\times 60\times 10\text{-mm}$ structural angle has the following cross-sectional properties: $I_x=0.808\times {10}^6{\text{mm}}^4,I_y=0.388\times {10}^6{\text{mm}}^4,$ and $I_2=0.213\times {10}^6{\text{mm}}^{\text{4}},$ where $I_2$ is a centroidal principal moment of inertia. Assuming that $I_{xy}$ is negative, compute (a) $I_1$ (the other centroidal principal moment of inertia); and (b) the principal directions at the centroid.