In ∆DEF, ∠F = ∠D and EF = 4 cm and DF = 5 cm. Then find the length of DE

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.

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step-by-step explanati∵∵∴∴on: