MathDB

1

Part of 2015 South Africa National Olympiad

Problems(1)

Points $E$ and $F$ inside a square $ABCD$

Source:

8/8/2015
Points EE and FF lie inside a square ABCDABCD such that the two triangles ABFABF and BCEBCE are equilateral. Show that DEFDEF is an equilateral triangle.
geometry