Answers

2015-05-27T12:34:29+05:30
n(n-3)/2    which is the required formula 
1.convex quadrilateral
n=4
4(4-3)/2=4/2=2
ans=2

2.regular hexagon
 n=6
6(6-3)/2=6(3)/2=18/2=9
ans=9
3.triangle 
 n=3
3(3-3)/2=0/2=0
ans =0
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