Question 359501
<pre>
There are n exterior angles and n interior angles.

Each exterior angle is supplementary to an interior angle.

At each of the n corners there is a linear pair consisting of
an interior angle and an exterior angle.  That's n×180°, as the
sum of all interior and exterior angles.

The sum of the n interior angles is (n-2)×180°

Subtract the sum of the interior angles from the sum of the 
n linear pairs at the corners, which is the sum of all
interior and exterior angles, and that will leave the sum of
the exterior angles.

n×180° -  (n-2)×180° = [n-(n-2)]×180° = [n-n+2]×180° = 2×180° = 360°

Edwin</pre>