D and E are the mid-points of the sides BC and AB respectively of ΔABC.
∴DE∥BA, DE=12×BA [ Mid-point theorem]
⇒DE∥FA……(1)
Since, D and F are mid-points of the sides BC and AB respectively of ΔABC,
∴DF∥CA⇒DF∥AE....(2)
From (1) and (2) we conclude that AFDE is a parallelogram
Similarly, BDEF is a parallelogram
Now, in ΔDEF and ΔABC, we have
∠FDE=∠A [Opposite angles of parallelogram AFDE]
and ∠DEF=∠B [Opposite angles of parallelogram BDEF]
⇒ΔDEF∼ΔABC [AA-similarity criterion]
⇒Area (ΔDEF)Area (ΔABC)=DE2AB2
⇒Area (ΔDEF)Area (ΔABC)=(12AB)2AB2=14
[∵DE=12×AB]
Hence, Area (ΔDEF):Area (ΔABC)=1:4