document.write( "Question 558343: how many diagonals are in a Decagon \n" ); document.write( "

Algebra.Com's Answer #363041 by Theo(13342) $\"\"$ $\"About$

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the number of diagonals in a polygon are given by the equation:
\n" ); document.write( "(n * (n-3))/2
\n" ); document.write( "for your decagon, the number of sides is equal to 10.
\n" ); document.write( "this makes the formula:
\n" ); document.write( "(10 * 7)/2 which becomes 35.
\n" ); document.write( "you can see the formula working in smaller polygons.
\n" ); document.write( "for a quadrilateral the number of diagonals is clearly 2.
\n" ); document.write( "(4 * 1) / 4 / 2 = 2
\n" ); document.write( "for a pentagon the number of diagonals is clearly 5
\n" ); document.write( "(5 * 2) / 2 = 10 / 2 = 5
\n" ); document.write( "for a hexagon the number of diagonals is not so clearly 9 (it's getting harder to count them but the number is definitely 9).
\n" ); document.write( "(6 * 3) / 2 = 18 / 2 = 9
\n" ); document.write( "see the following reference for more information:
\n" ); document.write( "http://www.math.com/tables/geometry/polygons.htm \n" ); document.write( "

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