A polygon has 44 diagonals the number of its sides is?

• A. 10
• B. 11
• C. 12
• D. 9

Answer: (B)

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