Mock AIME 1 2006-2007 Problems/Problem 8
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Problem
Let be a convex pentagon with
,
,
, and
. If
where
and
are relatively prime positive integers, find
.
Solution
![[asy]defaultpen(fontsize(8)); pair A=expi(pi*5/12)+expi(0)+expi(pi/2), B=expi(pi*5/12), C=(0,0), D=expi(0), E=expi(0)+expi(pi/12), P=expi(pi*5/12)+expi(0); draw(A--B--C--D--E--A);draw(B--P--E--B);draw(D--P--A); label("A",A,(1,0));label("B",B,(-1,0));label("C",C,(-1,0));label("D",D,(1,-1)); label("E",E,(1,0));label("P",P,(1,0)); dot(A^^B^^C^^D^^E^^P);[/asy]](http://latex.artofproblemsolving.com/7/5/a/75a1a47b166889a6586a8ba9f1ef40758ff387ae.png)
Let be a point in
such that
. We see that
and thus
. Since
, we have that
is a rhombus. Therefore
so
. Since
we have that
is equilateral.
.
.