



 
Greg, Here's some hints on how to get going. First observe that if two of your points are diagonally opposite you do not have an acute triangle  what is it? So any choice of 3 points with a diagonally opposite pair have to be excluded. For the rest, look at one of your points and the diagonally opposite point (which is not among your selection). Your other 2 points are either both on one side of this diagonal or one on each side  which corresponds to an acute triangle? Penny
 


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 