You can put this solution on YOUR website! Create the altitude by bisecting the apex angle with a line that also bisects the base creating two 30-60-90 triangles.
30-60-90 triangles have sides with a ratio of 1, sqrt(3) and 2.
1/2 * ab = A
a=bsqrt(3) for one of the 30-60-90 triangles.
1/2 * b*bsqrt(3)=18sqrt(3)
b^2sqrt(3)=36sqrt(3)
b^2=36
b=6
6*2=12 length of one side of the equilateral triangle.
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Ed
