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Sorry, I'll erase my point because it's just a mess.

Only quadrangles have a angle sum of 360Â°, according to the formula (n-2)180. But it's funny that, while calculating with the angle sum of a quadrangle, I haven't even noticed that this supposition contradicts the result with n=9.

Sorry that I confused you

Last edited by allabout on 01 Feb 2006, 08:04, edited 1 time in total.

I agree with ps_dahiya's solution. X and Y have to be angles made with the paper, otherwise we will get n = 18/7.

2*a+X+Y = 360 (we know that it is a quadrilateral)

X+Y = 80

=> a = 140.

Sum of all angles = (n-2)*180

Each angle = (n-2)*180/n

(n-2)*180/n = 140

Hence n = 9 _________________

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