2009 AMC 8 Problems/Problem 9

Problem

Construct a square on one side of an equilateral triangle. One on non-adjacent side of the square, construct a regular pentagon, as shown. One a non-adjacent side of the pentagon, construct a hexagon. Continue to construct regular polygons in the same way, until you construct an octagon. How many sides does the resulting polygon have?

$[asy] defaultpen(linewidth(0.6)); pair O=origin, A=(0,1), B=A+1*dir(60), C=(1,1), D=(1,0), E=D+1*dir(-72), F=E+1*dir(-144), G=O+1*dir(-108); draw(O--A--B--C--D--E--F--G--cycle); draw(O--D, dashed); draw(A--C, dashed);[/asy]$

$\textbf{(A)} 21 \qquad \textbf{(B)} 23 \qquad \textbf{(C)} 25 \qquad \textbf{(D)} 27 \qquad \textbf{(E)} 29$

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2009 AMC 8 Problems/Problem 9

Problem