Answer :

icarlson
well you have to use the equation     (n-2(180))  where n represents the number of sides  

so-    21 - 2 = 19      then multiply    19 x 180 = 3420

so the sum of all the interior angles in a 21-gon is equal to    3420 degrees
calculista
we know that
Sum of the measures of the interior angles of a polygon of n sides is equal to

[tex](n-2)*180[/tex]

where
n is the number of sides

in this problem
[tex]n=21 \\ (21-2)*180=3420[/tex]°

Hence

sum of the measures of the interior angles of a 21 sided polygon is
[tex]3420[/tex]°

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