Question

In AABC, the altitude AD , BE and CF are equal. Prove that AABC is an equilateral triangle.​

Answer 1

In right-angle triangles BCE and CBF, we have,

BC = BC (common hypotenuse);

BE = CF (given).

Hence BCF and CBF are congruent, by RHS theorem. Comparing the triangles, we get ∠B=∠C.

This implies that

AC = AB (sides opposite to equal angles).

Similarly,

AD=BE⇒∠B=∠A

⇒AC=BC

Together, we get AB=BC=ACor △ABC is equilateral. [hence proved]