Pentagon Geometry
Source: AHSME 1986 problem 28
October 2, 2011
geometryAMC
Problem Statement
is a regular pentagon. , and are the perpendiculars dropped from onto , extended and extended, respectively. Let be the center of the pentagon. If , then equals[asy]
size(200);
defaultpen(fontsize(10pt)+linewidth(.8pt));
pair O=origin, A=2*dir(90), B=2*dir(18), C=2*dir(306), D=2*dir(234), E=2*dir(162), P=(C+D)/2, Q=C+3.10*dir(C--B), R=D+3.10*dir(D--E), S=C+4.0*dir(C--B), T=D+4.0*dir(D--E);
draw(A--B--C--D--E--A^^E--T^^B--S^^R--A--Q^^A--P^^rightanglemark(A,Q,S,7)^^rightanglemark(A,R,T,7));
dot(O);
label("",O,dir(B));
label("",(O+P)/2,W);
label("",A,dir(A));
label("",B,dir(B));
label("",C,dir(C));
label("",D,dir(D));
label("",E,dir(E));
label("",P,dir(P));
label("",Q,dir(Q-A));
label("",R,dir(R-A));
[/asy]