Problem 173.
Quadrilateral with Midpoints, Triangles, Areas.

In the figure below, ABCD is a
quadrilateral with E, and F, midpoints of BC, and
AD respectively. Lines EA, ED, FB and FC determine the shaded
regions of areas S1,
S2,
S3,
and S4.
Prove that S1
+
S2
= S3
+
S4.
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