Answer:
(b) ED + EF < DF
Step-by-step explanation:
You want to know why DE = 1/2DF, FE = 1/3DF, and DF cannot be used to form a triangle.
The triangle inequality requires the sum of the two short sides of a triangle exceed the length of the long side. Here, that would require ...
ED + EF > DF
However, we have ...
(1/2)DF + (1/3)DF = (5/6)DF < DF
The short sides total a length less than DF, so cannot be used to form a triangle.
ED +EF < DF . . . . . choice B