Answers

2016-04-26T20:07:41+08:00
A regular octagon can be divided into 8 regular isoceles  triangles
the top angle of the triangle =   360/8 =  45°
thus the top angle of the right triangle =  45/2°
     using the right triangle to find the side we have
         tan 45/2  =   s/12       / in this case the apothem is the perpendicular
                                             height of the triangle /  s = side of the right triangle                 s =  12 tan 45/2
                    = 12 * .4142   =  4.9704 cm
                thus the length of the side =   4.9704 * 2
                                                              ≈   9.9408 cm
               note: if you draw an isoceles triangle with the apothem
                         you will have a better understanding of my explaination

 
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