The shear strain ${\gamma }_{nt}$ is computed from:

$$\begin{gathered} {\gamma }_{nt}=-2 ({\epsilon }_x-{\epsilon }_y) \sin \theta \cos \theta +{\gamma }_{xy} ({\cos }^2\theta -{\sin }^2\theta ) \\ =-2 \left[\left(900\mu \right)-(-600\mu )\right] \sin \left({50}^{\circ }\right) \cos \left({50}^{\circ }\right) \\ +(-850\mu )\left[{\cos }^2\left({50}^{\circ }\right)-{\sin }^2\left({50}^{\circ }\right)\right] \\ =-1,329.61 \mu m/m \end{gathered}$$