Suppose that the side length is s. Imagine that one side is level. Draw a vertical line through the top vertex perpendicular to the base (level side). Label this vertical line "h." Then h and s are related as follows:
√3 h
sin 60 degrees = ------- = --------
2 s
s√3
and so h = the height of the triangle = -----------
2
The area of this triangle is (1/2)(base)(height), which here is: