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AMC 12 2018b Problem 25

  • Paper

Circles ω1\omega_1, ω2\omega_2, and ω3\omega_3 each have radius 44 and are placed in the plane so that each circle is externally tangent to the other two. Points P1P_1, P2P_2, and P3P_3 lie on ω1\omega_1, ω2\omega_2, and ω3\omega_3 respectively such that P1P2=P2P3=P3P1P_1P_2=P_2P_3=P_3P_1 and line PiPi+1P_iP_{i+1} is tangent to ωi\omega_i for each i=1,2,3i=1,2,3, where P4=P1P_4 = P_1. See the figure below. The area of △P1P2P3\triangle P_1P_2P_3 can be written in the form a+b\sqrt{a}+\sqrt{b} for positive integers aa and bb. What is a+ba+b?

unitsize(12);
pair A = (0, 8/sqrt(3)), B = rotate(-120)*A, C = rotate(120)*A;
real theta = 41.5;
pair P1 = rotate(theta)*(2+2*sqrt(7/3), 0), P2 = rotate(-120)*P1, P3 = rotate(120)*P1;
filldraw(P1--P2--P3--cycle, gray(0.9));
draw(Circle(A, 4));
draw(Circle(B, 4));
draw(Circle(C, 4));
dot(P1);
dot(P2);
dot(P3);
defaultpen(fontsize(10pt));
label("P1P_1", P1, E*1.5);
label("P2P_2", P2, SW*1.5);
label("P3P_3", P3, N);
label("ω1\omega_1", A, W*17);
label("ω2\omega_2", B, E*17);
label("ω3\omega_3", C, W*17);

(A) 546(B) 548(C) 550(D) 552(E) 554\textbf{(A) }546 \textbf{(B) }548 \textbf{(C) }550 \textbf{(D) }552 \textbf{(E) }554

Dataset text AMC 12 2000 to 2025. Quoted with source.

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D

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