The sum of the angles of a regular n-sided polygon is equal to (n - 2) x 180 degrees.
Therefore, the sum of the angles of a regular 40-sided polygon (tetradecagon) is equal to (40 - 2) x 180 = 6840 degrees. Therefore, 6840 refers to the sum of the degrees, not the number of diagonals.
The number of diagonals of an n-sided polygon is given by n(n-3)/2. So a 40-sided polygon has 40*37/2=740 diagonals.
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180*(40-2) = 180*38 = 6840 degrees.
There are: (6840+360)/180 = 40 sides
740 The number of digaonals is given by n(n-3)/2, where n is the number of sides (or vertices) of a polygon: 40(40-3)/2=20*37=740 For a proof, see: http://www.artofproblemsolving.com/Wiki/index.php/Diagonal
tetracontahedron
40-gon.