Side AC is aligned with the $x$ axis; therefore, ${\theta }_{AC}=0^{\circ }$

Write a strain transformation equation for side AC:

$+1,250\mu \epsilon ={\epsilon }_x {\cos }^2\left(0\right)+{\epsilon }_y {\sin }^2\left(0\right)+{\gamma }_{xy} \sin \left(0\right)\cos \left(0\right)$

Since $\sin \left(0\right)=0$ and $\cos \left(0\right)=1$, this equation simplifies to: