There is a theorem which states that "If the areas of two similar triangles are equal then the triangles are congruent."
So, the longest side of Δ DEF will be congruent to ΔABC.
Longest side of Δ DEF ≡ Longest side of ΔABC.
Suppose in the diagram, the longest side of the Δ DEF is EF and longest side of Δ ABC is BC.
So, EF = BC
Since, EF= 25 units is given.
So, BC= 25 units.
Hence, longest side of triangle ABC is 25 units.
