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If two altitudes of a triangle are equal, prove that it is an isosceles triangle.

If two altitudes of a triangle are equal, prove that it is an isosceles triangle. R.S. Aggarwal Mathematics Solutions ICSE Class 9.

Triangles

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Answer

Given,

CE = BD [Altitudes of △ABC are equal]

In △ABD and △ACE,

⇒ ∠ADB = ∠AEC [Each equal to 90°]

⇒ CE = BD [Given]

⇒ ∠DAB = ∠EAC [Common angle]

∴ △ABD ≅ △ACE (∵ A.A.S. axiom)

⇒ AB = AC [Corresponding parts of congruent triangles are equal]

Since, two sides are equal.

Hence, △ABC is an isosceles triangle with AB = AC.

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