Area Fiesta!!

Level pending

In square A B C D ABCD , one of the vertices of square A J P I AJPI touches E H \overline{EH} at P P and E H \overline{EH} and F G \overline{FG} are tangent to the two congruent circles at P P and Q Q respectively and the radius of each circle is half the side of the square A J P I AJPI .

Let A T A_{T} be the area of the pink shaded regions.

Find A T A A B C D \dfrac{A_{T}}{A_{ABCD}} .


The answer is 0.35297886967.

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1 solution

Rocco Dalto
Dec 13, 2020

Using the diagram above A C = 2 a = 2 x + x + x 2 + x 2 \overline{AC} = \sqrt{2}a = \sqrt{2}x + x + \dfrac{x}{2} + \dfrac{x}{\sqrt{2}} \implies

4 a = ( 6 + 3 2 ) x x = 4 a 6 + 3 2 = 4 a 3 2 ( 2 + 1 ) 4a = (6 + 3\sqrt{2})x \implies x = \dfrac{4a}{6 + 3\sqrt{2}} = \dfrac{4a}{3\sqrt{2}(\sqrt{2} + 1)} = 2 2 ( 2 1 ) 3 a = \dfrac{2\sqrt{2}(\sqrt{2} - 1)}{3}a

= 4 2 2 3 a = \dfrac{4 - 2\sqrt{2}}{3}a and C Q = x 2 + x 2 = \overline{CQ} = \dfrac{x}{2} + \dfrac{x}{\sqrt{2}} = 2 + 2 2 2 x = 2 ( 2 + 1 ) 2 2 x = \dfrac{2 + \sqrt{2}}{2\sqrt{2}}x = \dfrac{\sqrt{2}(\sqrt{2} + 1)}{2\sqrt{2}}x =

2 + 1 2 x = ( 2 + 1 2 ) ( 4 2 2 3 ) a = 2 3 a \dfrac{\sqrt{2} + 1}{2}x = (\dfrac{\sqrt{2} + 1}{2})(\dfrac{4 - 2\sqrt{2}}{3})a = \dfrac{\sqrt{2}}{3}a

F C G \triangle{FCG} is a right isosceles triangle F Q Q G F Q C C Q G \implies \overline{FQ} \cong \overline{QG} \implies \triangle{FQC} \cong \triangle{CQG} \implies

A F C G = 2 A F Q C = 2 ( 1 2 ( C Q ) 2 ) = 2 9 a 2 A_{\triangle{FCG}} = 2 A_{\triangle{FQC}} = 2(\dfrac{1}{2}(\overline{CQ})^2) = \dfrac{2}{9}a^2

and A A E H = 2 A A E P = 2 ( 1 2 ) ( 2 x ) 2 = 2 x 2 = 2 9 ( 4 2 2 ) 2 a 2 = A_{\triangle{AEH}} = 2A_{\triangle{AEP}} = 2(\dfrac{1}{2})(\sqrt{2}x)^2 = 2x^2 = \dfrac{2}{9}(4 - 2\sqrt{2})^2a^2 =

2 9 ( 24 16 2 ) a 2 \dfrac{2}{9}(24 - 16\sqrt{2})a^2

Let A s = A F C G + A A E H = 2 9 ( 25 16 2 ) a 2 A_{s} = A_{\triangle{FCG}} + A_{\triangle{AEH}} = \dfrac{2}{9}(25 - 16\sqrt{2})a^2

The area of circle A c = π r 2 = π ( x 2 ) 2 = π 9 ( 2 2 ) 2 a 2 = A_{c} = \pi r^2 = \pi(\dfrac{x}{2})^2 = \dfrac{\pi}{9}(2 - \sqrt{2})^2a^2 = 2 π 9 ( 3 2 2 ) a 2 \dfrac{2\pi}{9}(3 - 2\sqrt{2})a^2

Let A = A s + A c = 2 9 ( 25 16 2 + ( 3 2 2 ) π ) a 2 A^{*} = A_{s} + A_{c} = \dfrac{2}{9}(25 - 16\sqrt{2} + (3 - 2\sqrt{2})\pi)a^2 \implies

A T = a 2 A = 32 2 41 2 ( 3 2 2 ) π 9 a 2 A_{T} = a^2 - A^{*} = \dfrac{32\sqrt{2} - 41 - 2(3 - 2\sqrt{2})\pi}{9}a^2 \implies

A T A A B C D = 32 2 41 2 ( 3 2 2 ) π 9 0.35297886967 \dfrac{A_{T}}{A_{ABCD}} = \dfrac{32\sqrt{2} - 41 - 2(3 - 2\sqrt{2})\pi}{9} \approx \boxed{0.35297886967} .

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