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2009 AMC 8 Problems/Problem 20

Revision as of 12:28, 14 August 2011 by Mrdavid445 (talk | contribs)

Problem

How many non-congruent triangles have vertices at three of the eight points in the array shown below?

[asy]dot((0,0)); dot((0,.5)); dot((.5,0)); dot((.5,.5)); dot((1,0)); dot((1,.5)); dot((1.5,0)); dot((1.5,.5));[/asy]

$\textbf{(A)}\ 5 \qquad \textbf{(B)}\ 6 \qquad \textbf{(C)}\ 7 \qquad \textbf{(D)}\ 8 \qquad \textbf{(E)}\ 9$

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