Physics
posted by Please Help! .
The three 500 g masses in the daigram are connected by massless, rigid rods to form a triangle. What is the triangle's rotational energy (in J) if it rotates at 1.50 rev/s about an axis through the center?
(Diagram shows equilateral triangle with 500g masses at each point, the distance from point to point is 40cm and it has three 60deg angles [equilateral])
I keep getting the same thing and it's wrong

energy= 1/2 I w^2
I= 3*mx^2 where cos30=x/.2meter
m= .5kg
w=1.50*2PI rad/sec 
I do not understand the part in which you solve for x. Is it supposed to be the cos of 60 equals x divided by .2?