In an equilateral triangle, prove that the centroid and the circumcentre of triangle coincide. In the chapter circle of class 9
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Answer:
proved : The centroid and circumcentre are coincident.
Step-by-step explanation:
Given : An equilateral triangle ABC in which D, E and F are the mid- points of sides BC,
CA and AB respectively.
Construction : Draw medians, AD, BE and CF.
Proof : Let G be the centroid of ΔABC i. e., the point of intersection of AD, BE and CF. In triangles BEC and BFC, we have
∠B = ∠C = 60
BC = CE [∵ AB = AC ⇒ ½ AB = ½ AC ⇒ BF = CE]
∴ ΔBEC ≅ ΔBFC
⇒ BE = CF ……(i)
Similarly, ΔCAF ≅ ΔCAD
CF = AD …….(ii)
From (i) & (ii) AD = BE = CF
⇒ 2/3 AD = 2/3, BE = 2/3 CF
CG = 2/3 CF
GA = 2/3 AD, GB = 2/3 BE
⇒ GA = GB = GC
⇒ G is equidistant from the vertices
⇒ G is the circumcentre of ΔABC
Hence, the centroid and circumcentre are coincident.
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