Let ABC be an equilateral triangle of side 9cm and let AD one of its medians. Let G be the centroid of ΔABC.
Then AG : GD = 2:1
WKT in an equilateral Δle centroid coincides with the circum center
Therefore, G is the center of the circumference with circum radius GA
Also G is the center and GD ⊥ BC .
Therefore,
In right triangle ADB, we have