P.1.10. In Fig. P.1.10, the direct strains in the directions a, b, c are -0.002, -0.002, and +0.002,respectively. If I and II denote principal directions, find ɛ1, E, and 0.

\text { Answer: } \quad \varepsilon_{\mathrm{I}}=+0.00283, \quad \varepsilon_{\mathrm{II}}=-0.00283, \quad \theta=-22.5^{\circ} \text { or }+67.5^{\circ}