HKIMO 2018 Grade 5 National Final (Heat) Set 03 Question 20

$ABDF$ is a square, and triangles $FDE$ and $BDC$ are right isosceles triangles. Find the area of $ACDE$.



Source glossary (English–Vietnamese): Square: hình vuông; Right angle isosceles triangles: các tam giác vuông cân; Area: diện tích.