Q.

If the length of median of an equilateral triangle be x,   then its area is


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a

     x 2  

b

     3 2 x 2  

c

     x 2 3  

d

     x 2 2   

answer is C.

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Detailed Solution

We have been given an equilateral triangle ABC such that the length of median is x.   Sides AB and AC and median AD of a triangle ABC are class 10 maths CBSE AD=x   We know that the median is also an altitude in the equilateral triangle.
Let a   be the side of the triangle. So,
AB=BC=AC=a  
Since AD is the median of ΔABC,    therefore, we have,
BD =  a 2  cm   In right ΔADB,   we have,
 AB 2 =B D 2 +A D 2  
a 2  =  a 2 2 + x 2  
x 2 = 3 a 2 4  
x= 3 2 a a= 2x 3  
 We know that,
Area of ΔABC= 1 2 ×b×h Area of ΔABC= 1 2 × 2x 3 ×x Area of ΔABC= x 2 3  
Therefore, if the length of median of an equilateral triangle be x  , then its area is x 2 3 .  
Hence, option (3) is correct.
 
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