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Number of diagonals in a polygon with n sides:

An!
Bn² - n
CCannot determine
Dn(n-3)/2
Answer & Solution
Correct answer: D. n(n-3)/2
Total line segments connecting any 2 of n vertices = C(n,2). **Subtract n sides:** n(n-1)/2 - n = (n² - n - 2n)/2 = n(n-3)/2. For hexagon (n=6): 6×3/2 = 9 diagonals.
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