Answer:
DE = 4cm.
Step-by-step explanation:
The Isoscles Triangle Theorem says that:
"If two sides of a triangle are congruent, then angles opposite those sides are congruent."
The converse of this theorem is
"If angles opposite those sides are congruent, then two sides of a triangle are congruent."
Therefore, since ∠F is congruent to ∠D and are opposite sides ED and EF
while EF = 4 cm and DF = 5 cm.
DE = 4cm.
