For a better understanding of the solution provided here, please find the diagram attached.
In the diagram, ABCD is the room.
AC is the diagonal whose length is 18.79 inches.
The length of wall AB is 17 inches.
From the given information, we have to determine the length of the BC, which is depicted a , because for the room to be a square, the length of the wall AB must be equal to the length of the wall BC.
In order to determine the length of the wall BC, or , we will have to employ the Pythagoras' Theorem here. Thus:
Thus, inches
and hence, the given room is not a square.