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Difference between revisions of "2022 AIME I Problems/Problem 8"
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.==solution 1==
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== Problem ==
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Equilateral triangle <math>\triangle ABC</math> is inscribed in circle <math>\omega</math> with radius <math>18.</math> Circle <math>\omega_A</math> is tangent to sides <math>\overline{AB}</math> and <math>\overline{AC}</math> and is internally tangent to <math>\omega</math>. Circles <math>\omega_B</math> and <math>\omega_C</math> are defined analogously. Circles <math>\omega_A</math>, <math>\omega_B</math>, and <math>\omega_C</math> meet in six points<math>-</math>two points for each pair of circles. The three intersection points closest to the vertices of <math>\triangle ABC</math> are the vertices of a large equilateral triangle in the interior of <math>\triangle ABC</math>, and the other three intersection points are the vertices of a smaller equilateral triangle in the interior of <math>\triangle ABC</math>. The side length of the smaller equilateral triangle can be written as <math>\sqrt{a}-\sqrt{b}</math>, where <math>a</math> and <math>b</math> are positive integers. Find <math>a+b</math>.
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 +
== Diagram ==
 +
<asy>
 +
unitsize(0.3cm);
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draw(circle((0,0),18));
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pair A = (9 * sqrt(3), -9);
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pair B = (-9 * sqrt(3), -9);
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pair C = (0,18);
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draw(A--B--C--cycle);
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draw(circle((0,-6),12), gray);
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draw(circle((3*sqrt(3),3),12), gray);
 +
draw(circle((-3*sqrt(3),3),12), gray);
 +
 
 +
pair X = (0, 3-sqrt(117));
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pair Y = ( (sqrt(351)-sqrt(27))/2, (sqrt(117)-3)/2 );
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pair Z = ( (sqrt(27) - sqrt(351))/2, (sqrt(117)-3)/2 );
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dot(X);
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dot(Y);
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dot(Z);
 +
 
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draw(X--Y--Z--cycle, dashed);
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</asy>
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 +
==Solution==
  
 
Let bottom left point as the origin, the radius of each circle is <math>36/3=12</math>, note that three centers for circles are <math>(9\sqrt{3},3),(12\sqrt{3},12),(6\sqrt{3},12)</math>
 
Let bottom left point as the origin, the radius of each circle is <math>36/3=12</math>, note that three centers for circles are <math>(9\sqrt{3},3),(12\sqrt{3},12),(6\sqrt{3},12)</math>
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~bluesoul
 
~bluesoul
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 +
==See Also==
 +
{{AIME box|year=2022|n=I|num-b=7|num-a=9}}
 +
{{MAA Notice}}

Revision as of 20:17, 17 February 2022

Problem

Equilateral triangle $\triangle ABC$ is inscribed in circle $\omega$ with radius $18.$ Circle $\omega_A$ is tangent to sides $\overline{AB}$ and $\overline{AC}$ and is internally tangent to $\omega$. Circles $\omega_B$ and $\omega_C$ are defined analogously. Circles $\omega_A$, $\omega_B$, and $\omega_C$ meet in six points$-$two points for each pair of circles. The three intersection points closest to the vertices of $\triangle ABC$ are the vertices of a large equilateral triangle in the interior of $\triangle ABC$, and the other three intersection points are the vertices of a smaller equilateral triangle in the interior of $\triangle ABC$. The side length of the smaller equilateral triangle can be written as $\sqrt{a}-\sqrt{b}$, where $a$ and $b$ are positive integers. Find $a+b$.

Diagram

[asy] unitsize(0.3cm); draw(circle((0,0),18)); pair A = (9 * sqrt(3), -9); pair B = (-9 * sqrt(3), -9); pair C = (0,18); draw(A--B--C--cycle); draw(circle((0,-6),12), gray); draw(circle((3*sqrt(3),3),12), gray); draw(circle((-3*sqrt(3),3),12), gray); pair X = (0, 3-sqrt(117)); pair Y = ( (sqrt(351)-sqrt(27))/2, (sqrt(117)-3)/2 ); pair Z = ( (sqrt(27) - sqrt(351))/2, (sqrt(117)-3)/2 ); dot(X); dot(Y); dot(Z); draw(X--Y--Z--cycle, dashed); [/asy]

Solution

Let bottom left point as the origin, the radius of each circle is $36/3=12$, note that three centers for circles are $(9\sqrt{3},3),(12\sqrt{3},12),(6\sqrt{3},12)$

It is not hard to find that one intersection point lies on $\frac{\sqrt{3}x}{3}$ since the intersection must lie on the angle bisector of the bigger triangle, plug it into equation $(x-9\sqrt{3})^2+(\frac{\sqrt{3}x}{3}-3)^2=12^2$, getting that $x=\frac{15\sqrt{3}+3\sqrt{39}}{2}$, the length is $2*(\frac{15\sqrt{3}+3\sqrt{39}-18\sqrt{3}}{2}=3\sqrt{39}-3\sqrt{3}$, leads to the answer $378$

~bluesoul

See Also

2022 AIME I (Problems • Answer Key • Resources)
Preceded by
Problem 7 		Followed by
Problem 9
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15
All AIME Problems and Solutions

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