In the adjoining diagram, is a square. The larger circle has center which is also the center of the square. The smaller circles have equal radii and are each tangent to the square and the larger circle. The area of the larger circle is equal to the sum of the areas of the smaller four circles. What is the ratio between the side length of the square and the radius of a smaller circle?
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If the radius of the large circle is R and that of the small circles is r , we have π R 2 = 4 π r 2 or R = 2 r .
So the distance O R = 3 r .
The line O R is a part of the diagonal and at 4 5 ∘ angle with the vertical, so its projection into the vertical, E R = 3 r c o s ( 4 5 ∘ ) = 2 3 r .
Add to this the distance R T = r and we’ll have half the side of the square, a .
Therefore a = 2 ( 2 3 r + r ) = r ( 2 + 3 2 ) and the ration r a = 2 + 3 2 .