Correct Option
The number of diagonals in any polygon with 'n' vertices (or sides) is calculated using the formula: 2n(n−3).
For an octagon, the number of sides (n) is 8.
Substituting n = 8 into the formula yields:
28(8−3)=28×5=240=20
Therefore, an octagon has 20 diagonals.
Incorrect Options
Options 2 (24), 3 (28), and 4 (64) are incorrect. These values do not correspond to the number of diagonals in an octagon as determined by the standard geometric formula 2n(n−3).