The area of a triangle can be obtained by:
Try using the second formula, where c is the angle between the sides a and b.
Post what you get.
I prefer not doing the calculations, because I don't quite understand your question. I especially don't know what the square has to do with the area of the triangle...
EDIT: Remember that in an equilateral triangle, all the angles within the triangle are 60 degrees, so c = 60