I don't think this question itself is correct
number of diagonals in n sided polygon = n*(n-3)/2
none of answer choices bring 78
could you please reconfirm?
thanks
satish.
polygon
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satish.nagdev
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x2suresh
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moadhia wrote:In a Polygon,all but one vertices are connected to each other by straight lines and 78 diagonals are formed.How many sides does the polygon have ?
A. 15
B.17
C.12
D.16
E.18
I dont have an OA for this.
Let n+1 points in the polygon
One vertex is not connected to ..any of the other vertex
so.. Its like polygon with N sides and the link is broken.
Forumula for No.Of diagnols = NC2(select any two points out of N) -N (substracting sides )
Here No.Of diagonals=NC2 -(N-1) ( here one of them is actually not side it is diagnol .. )
N (N-3)/2 = 78 -1 = 77 = 11*14/2
N = 14
N+1 = 15
A is the Answer.
Last edited by x2suresh on Thu Feb 26, 2009 10:27 am, edited 1 time in total.
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satish.nagdev
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awesome Suresh 
I din't paid attention properly to all but one thing
thanks for clarifying
cheers,
satish
I din't paid attention properly to all but one thing
thanks for clarifying
cheers,
satish
