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/_ |_\ as you notice the height is the perpendicular in the middle of the rectangle so let us call it h and each leg length=x
you can devide the triangle into two seperate triangles of angles 90-60-30 since it is an equilateral triangle it has the same length for its three legs so the height = tan(60)=h/(x/2)
tan(60)= sqrt(3)--->sqrt(3)=(2h)/x--->sqrt(3)/2=h/x
h=x*sqrt(3)/2
