Problem #2186


Circles with centers $O$ and $P$ have radii $2$ and $4$, respectively, and are externally tangent. Points $A$ and $B$ on the circle with center $O$ and points $C$ and $D$ on the circle with center $P$ are such that $AD$ and $BC$ are common external tangents to the circles. What is the area of the concave hexagon $AOBCPD$?

[asy] unitsize(.7cm); defaultpen(.8);  pair O = (0,0), P = (6,0), Q = (-6,0); pair A = intersectionpoint( arc( (-3,0), (0,0), (-6,0) ), circle( O, 2 ) ); pair B = (A.x, -A.y ); pair D = Q + 2*(A-Q); pair C = Q + 2*(B-Q);  draw( circle(O,2) ); draw( circle(P,4) ); draw( (Q + 0.8*(A-Q)) -- ( Q + 2.3*(A-Q) ) ); draw( (Q + 0.8*(B-Q)) -- ( Q + 2.3*(B-Q) ) ); draw( A -- O -- B ); draw( C -- P -- D ); draw( O -- P );  label("$O$",O,W); label("$P$",P,E);  label("$A$",A,NNW); label("$B$",B,SSW);  label("$D$",D,NNW); label("$C$",C,SSW); [/asy]

$\mathrm{(A) \ } 18\sqrt{3}\qquad \mathrm{(B) \ } 24\sqrt{2}\qquad \mathrm{(C) \ } 36\qquad \mathrm{(D) \ } 24\sqrt{3}\qquad \mathrm{(E) \ } 32\sqrt{2}$

This problem is copyrighted by the American Mathematics Competitions.

Note: you aren't logged in. If you log in, we'll keep a record of which problems you've solved.

Instructions for entering answers:

  • Reduce fractions to lowest terms and enter in the form 7/9.
  • Numbers involving pi should be written as 7pi or 7pi/3 as appropriate.
  • Square roots should be written as sqrt(3), 5sqrt(5), sqrt(3)/2, or 7sqrt(2)/3 as appropriate.
  • Exponents should be entered in the form 10^10.
  • If the problem is multiple choice, enter the appropriate (capital) letter.
  • Enter points with parentheses, like so: (4,5)
  • Complex numbers should be entered in rectangular form unless otherwise specified, like so: 3+4i. If there is no real component, enter only the imaginary component (i.e. 2i, NOT 0+2i).

For questions or comments, please email

Find out how your skills stack up!

Try our new, free contest math practice test. All new, never-seen-before problems.

AMC/AIME classes

I offer online AMC/AIME classes periodically. Join the mailing list to be informed next time they're offered.

Private coaching is also available.