It is given that the diagonal of a square is 12 inches.
The square is given by the diagram shown below:
In the triangle ABC by pythagorean theorem it follows:
[tex]\begin{gathered} AB^2+BC^2=AC^2 \\ 2AB^2=12^2 \\ AB^2=\frac{144}{2} \\ AB^2=72 \\ AB=\sqrt[]{72}=6\sqrt[]{2} \end{gathered}[/tex]Hence the side is given by:
[tex]s=6\sqrt[]{2}\text{ inches}[/tex]