J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer The number of diagonals of a polygon of 20 sides is

    A)  \[210\]           

    B)  \[190\]

    C)  \[180\]           

    D)  \[170\]

    Correct Answer: D

    Solution :

    Number of diagonals in a polygon of n sides \[{{=}^{n}}{{C}_{2}}-n\] Here, \[n=20\] \[\therefore \] Required number of diagonals \[{{=}^{20}}{{C}_{2}}-20\] \[=\frac{20\times 19}{2\times 1}-20\] \[=170\]


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