First, label the appropriate diagram of the parallelogram. If the diagonals are perpendicular to each other, then the sides of ABCD has to be 5.

use the equation for obtuse triangles

\(AB^2>25=3^2+4^2=AE^2+BE^2\)

all four angles around E, would be obtuse, which you can figure out to be impossible, so the side can't be longer than 5