The number of diagonals in a quadilateral = \(\frac{4\times(4-3)}{2}=2\)
The number of diagonals in a pentagon = \(\frac{5\times(5-3)}{2}=5\)
The number of diagonals in a hexagon = \(\frac{6\,\times\,3}{2}=9\)
The number of diagonals in a n sided = \(\frac{7\,\times\,4}{2}=14\)
The number of diagonals in a n sided polygon = \(\frac{n\times(n-3)}{2}=\frac{n(n-3)}{2}\)
