F5Math P&C

No. of diagonal of a n-sided polygon is C(n,2)-n

2012-04-12 09:13:33 補充：
Therefore,
C(n,2)-n=252
==> n^2-3n-504=0
==> (n-24)(n+21)=0
==> n=24

Ans : no. of sides is 24

252diagonals=504points=504sides

2012-04-12 09:13:18 補充：
誤會左對角線 應該係
(n^2-3n)/2=252
n^2-3n=504
n^2-3n-504=0
(n-24)(n+21)=0
n=24 or -21
由於係number of sides 不會係負數
所以n=24