¶ 2009 AMC8 Problem 20
Problem:
How many non-congruent triangles have vertices at three of the eight points in the array shown below?
Answer Choices:
A.
B.
C.
D.
E.
Solution:
With the points labeled as shown, one set of non-congruent triangles is and .
Every other possible triangle is congruent to one of the listed triangles.
: Find the distinct triangles possible and group them into sets of congruent triangles.
Answer: .
The problems on this page are the property of the MAA's American Mathematics Competitions