Q.

If the 3 altitudes of a triangle are equal, then triangle is:


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a

A scalene triangle

b

An isosceles triangle

c

An equilateral triangle

d

None of these 

answer is C.

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Detailed Solution

Given that the three altitudes of the triangle are equal.
So, AD = BF = CE.
Question ImageConsider triangles BEC and BFC  EC=BF   (Equal altitudes)
BEC=BFC= 90 o   (BE and BF are Altitudes)
BC=BC   (common)
ΔBECΔBFC   (RHS postulate)
ABC=BCA   (Corresponding angles)
Also,
Consider the ΔADB   and ΔADC  ,
  ADB=ADC= 90 o   (AD is altitude)
AD=AD   (common)
ABC = BCA   (proved above)
Thus, ADB   ADB (ASA postulate)
AB=AC   (Corresponding sides are equal)
Similarly, we can prove BFC BFA.
And, hence, BC=AC  .
Thus, AB=AC=BC  .
It implies that if the altitudes of the triangle are equal, then 3 sides of the triangle are also equal. So, the triangle will be an equilateral triangle.
Hence, the correct option is 3.
 
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