Determine the longest side in ΔDEF.
A) segment EF
B) segment DE
C) segment FE
D) segment DF

D Segment DF

The angle on the opposite side is the longest, so the line has to stretch the longest. The bigger the angle, the longer the line has to stretch.

So, since angle E is 73° which is larger than 43° and 64°. The line directly across from angle E is the longest.

Answer D . Segment DF is the longest.