An eight-sided polygon has 8 vertices. Consider
1st vertex = 7 diagonals to other vertices
2nd vertex = 6 diagonals to other vertices (since one has now been used)
3rd vertex = 5
4th vertex = 4
5th vertex = 3
6th vertex = 2
7th vertex = 1
8th vertex = 0, so
7+6+5+4+3+2+1 = 28
Improved Answer:-
Formula for finding diagonals of a polygon 0.5*(n2-3n) when n is the number of sides
0.5*(82-24) = 20 diagonals
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Well, honey, an 8-sided polygon, also known as an octagon, has a total of 20 diagonals. So, if you're feeling sassy and want to impress your friends with some polygon knowledge, there you have it!
A polygon can have 8 sides but does not have to. The word "Polygon" is made up of two words: "poly-" and "-gon" which have Greek roots which mean "many" and "angle" respectively; literally a "polygon" is a "many angled shape". A polygon is any shape that has 3 or more sides. An 8 sided polygon is called an octagon (literally "eight angles").
An octagon.octagon
A diagonal line of a polygon is a line that joins any two vertices not already joined by a side. A polygon with n sides has n(n-3)/2 diagonals → an octagon has 8(8-3)/2 = 8 × 5 ÷ 2 = 20 diagonals
The measure of 1 exterior angle of a regular 8-sided polygon is equivalent to 45 degrees. Hope I helped! :)
An octagon and a quadrilateral, respectively.