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  1. A polygon has 44 diagonals the number of its sides is ?
    1. 9
    2. 10
    3. 11
    4. 12
Correct Option: C

Let there be n sides of the polygon. Then it has n vertices.
The total number of straight lines obtained by joining n vertices by talking 2 at a time is nC2
These nC2 lines also include n sides of polygon.
Therefore, the number of diagonals formed is nC2 - n.
Thus, nC2 - n = 44
⇒ [n(n - 1)/2] - n = 44
⇒ ( n2 - 3n) / 2 = 44
⇒ n2 - 3n = 88
⇒ n2 - 3n - 88 = 0
⇒(n - 11) (n + 8) = 0
∴ n = 11



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