Question 260429
"What is the number of triangles formed in a decagon when all the diagonals from one vertex are drawn?" 
What does this mean and how do I figure it out? 
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look for a pattern:
4 sides (square): # of tiangles = 2
5 sides (pentagon): # of triangles = 3
6 sides (sexagon); # of triangles = 4
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10 sides (decagon: # of triangles = ?
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Cheers,
stan H.