bonanova 85 Posted October 29, 2010 Report Share Posted October 29, 2010 Each of three circles passes through the centers of the other two. The area interior to all three is quite close to, but different from, one quarter of the area A of a circle. Can you determine, through inference, construction or calculation, whether it's smaller or larger than A/4? Caveat: Arrgh. Forgot that I posted this problem before;* where it was solved by calculation. I'll bend the Den's rules a bit and leave it up, but modified. Please provide a purely geometrical solution. *A benefit of advancing age is the ability to hide one's own Easter eggs. Quote Link to post Share on other sites

0 Guest Posted October 29, 2010 Report Share Posted October 29, 2010 Less than 1/4. The ratio could be calculated as M = [3(/pi/6 R^2 -S) + S]/[(/pi) R^2] where S = /sqrt(3) R^2 /4 is the area of the triangle M = 1/2 - 2S/[(/pi) R^2] = 1/2 - /sqrt(3) /(2/pi) < 1/4 As /sqrt(3) >1.6 > 1/4 (2/pi) Quote Link to post Share on other sites

0 Guest Posted October 29, 2010 Report Share Posted October 29, 2010 Don't know how to draw but hope it's understandable: Let the center of the circles be A, B, C respectively and denote the intersecting point of circles A and B as M, that of A and C as N. Consider the the area of AMB and ANC, together they make 2S. MAN is a straight line and is the diameter of circle A. Move the parts of AMB and ANC which are outside of the half circle MANCB and paste it to BC, there's still a blank space in the half circle. Thus 2S < area of the half circle. S< 1/4 area of the circle. Quote Link to post Share on other sites

0 araver 10 Posted October 29, 2010 Report Share Posted October 29, 2010 Please provide a purely geometrical solution. Nice Easter Egg indeed Completing the picture with four more circles: So 1/4 of a circle is one blue + one red petal + one half blue + one half red petal And the area in question is one blue + one red petal + one red petal. We need to if either blue or red is the biggest. If red is biggest than Area >1/4 CircleArea, else Area <1/4 CircleArea. Construct another circle below to get a red petal inside the blue area. So 1/4 CircleArea > Area. Quote Link to post Share on other sites

0 Guest Posted October 29, 2010 Report Share Posted October 29, 2010 (edited) I used the area of a triangle (as an equilateral triangle with each leg being r, using Pythagorean theorem I got (r^2 sqrt(3))/4 , area of the circle (A = pi * r^2) and area of an arc segment (60' angle so 1/6*A) to get 1/2A - r^2*sqrt(3), which I don't know if it is bigger or smaller than 1/4A !!! I think it isn't... *edit: Maybe I was calculating too much and missed the point... I looked at the spoiler above this and saw pictures... back to the drawing board Edited October 29, 2010 by Asitaka Quote Link to post Share on other sites

## Question

## bonanova 85

Each of three circles passes through the centers of the other two.

The area interior to all three is quite close to, but different from, one quarter of the area A of a circle.

Can you determine, through inference, construction or calculation, whether it's smaller or larger than A/4?

Caveat:Arrgh. Forgot that I posted this problem before;* where it was solved by

calculation.I'll bend the Den's rules a bit and leave it up, but modified.

Please provide a

purely geometricalsolution.*A benefit of advancing age is the ability to hide one's own Easter eggs.

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