BC=6 EF=6

BF=4

therefore

EB=2

DE=2

So the shadow area is 1/2*2*2=2.

△ABC is an isosceles right triangle. No matter how it is translated, it is still an isosceles right triangle.

16 first empty △AOB translation.

Rectangular ABCD

Prove that △ODC is congruent △EDC

Get DE=AO。

CE=BO

So ... .

From 1. OE=BC=2