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 Apr 27, 2020
 #1
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There are 360o around each point.

Subtract the 72o to get 288o.

These degrees will be equally divided between the two polygons:  144o.

Using the  formula for the number of degrees in each interior angle of a regular polygon: 

                    [ (n - 2)·180] / n  =  144o

Solving:                (n - 2)·180o  =  144o·n

                         180o·n - 360o  =  144o·n

                                      36o·n  =  360o

                                             n  =  10

 Apr 27, 2020

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