Question

find the area of an equilateral triangle each of whose side is 10 cm

Answer 1

 s = 10+10+10/2
s= 15
a= 10 
b=10
c=10
using herons formula 
√s(s-a)(s-b)(s-c)
√15(15-10)(15-10)(15-10)
√15*5*5*5
5√15*5
5√5*3*5
25√3
area = 25√3cm^2

Answer 2

Ar of eq.tria = √3a/4
So,
√3*10*10/4= 25√3