The given figure is a square that measures 12 foot by 12 foot. please see illustration below;
The square in the sketch above shows the longest distance between two opposite diagonals, and that is the hypotenuse, labelled as a.
In the triangle ADC, using Pythagoras' theorem;
[tex]\begin{gathered} AD^2+DC^2=AC^2 \\ 12^2+12^2=a^2 \\ 144+144=a^2 \\ 288=a^2 \\ \sqrt[]{288}=a \\ a=16.97 \end{gathered}[/tex]The longest distance which is a (that is AC) is approximately 17 ft as shown above (16.97 ft).
