Let the side of the square = S
Connect the bottom left vertex of the large equilateral triangle with the vertex where the bottom square and leftmost square meet
This forms a 30-60-90 right traingle
We can find the distance from the bottom left vertex of the large equilateral square to the bottom left vertex of the bottom square = S* sqrt (3)
So....the side of the equilateral triangle is ( 2sqrt(3)S + S ) = S ( 2sqrt (3) + 1) = S [ sqrt (12) + 1 ]
And the side of the smaller equilateral triangle = S
The triangles are similar figures and their scale factor = [ S ] / [ S *( 2sqrt (3) + 1) ] = 1 / [ sqrt (12) + 1 ]
The ratio of the area of the smaller equilateral triangle to the larger = [ scale factor] ^2 =
[ 1 / [sqrt (12) + 1 ] ]^2 =
1 / [ 12 + 2sqrt (12) + 1 ] =
1/ [ 13 + 2sqrt (12) ] =
1/ [ 13 + sqrt (48) ] =
13 -sqrt (48)
___________ =
169 - 48
13 -sqrt (48)
_________ =
121
13 - 2sqrt (3)
___________ ≈ .05 ≈ 1/20
121
