Math Prize 2021 Problem 3
Source:
September 19, 2021
Math Prize for Girlsgeometry
Problem Statement
Let be the center of an equilateral triangle of area . As shown in the diagram below, a circle centered at meets the triangle at points , , , , , and , which trisect each of the triangle's sides. Compute the total area of all six shaded regions.
[asy]
unitsize(90);
pair A = dir(0);
pair B = dir(120);
pair C = dir(240);
draw(A -- B -- C -- cycle);
pair D = (2*A + B)/3;
pair E = (A + 2*B)/3;
pair F = (2*B + C)/3;
pair G = (B + 2*C)/3;
pair H = (2*C + A)/3;
pair I = (C + 2*A)/3;
draw(E -- F);
draw(G -- H);
draw(I -- D);
draw(D -- G);
draw(E -- H);
draw(F -- I);
pair O = (0, 0);
real r = 1/sqrt(3);
draw(circle(O, r));
fill(O -- D -- E -- cycle, gray);
fill(O -- F -- G -- cycle, gray);
fill(O -- H -- I -- cycle, gray);
fill(arc(O, r, -30, 30) -- cycle, gray);
fill(arc(0, r, 90, 150) -- cycle, gray);
fill(arc(0, r, 210, 270) -- cycle, gray);
label("", A, A);
label("", B, B);
label("", C, C);
label("", D, unit(D));
label("", E, unit(E));
label("", F, unit(F));
label("", G, unit(G));
label("", H, unit(H));
label("", I, unit(I));
label("", O, C);
[/asy]