Question 1207480
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        Your question is: Yes ?   (interrogative)


        My answer is:       Yes.    (affirmative)



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For first equation, you have

    {{{(n/2)*(n-3)}}} = 65

    n*(n-3) = 2*65

    n*(n-3) = 130

    and the solution / (the answer) is, OBVIOUSLY,  n= 13.


    It also can be done solving quadratic equation formally.




For second equation, you have

    {{{(n/2)*(n-3)}}} = 80

    n*(n-3) = 2*80

    n*(n-3) = 160.


Try to solve it formally as a quadratic equation,
and make sure that it does not have solution in integer positive numbers.
It means that such a polygon with precisely 80 diagonals does not exist.
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