Question

the sides of an equilateral triange are 4 cm long.what is the radius of its circumcircle?

Answer 1

radius of a circumcircle of an equilateral triangle r = s/√3
where s = side of triangle
 r = 4/√3
r = 2.309 ≈ 2.31 cm.

Answer 2

radius of a circumcircle is given by formula S/√3
so 
the radius is 4÷√3
=2.30940