How to calculate an angle in a regular polygon is quite simple. Take a look at the graphic below to see how it's done:

n = number of sides in a regular polygon.[br][br][math]\left(n-2\right)\times180=A^{\circ}[/math][br][br](A[math]^\circ[/math] is the sum of all the interior angles inside a regular polygon.)

A simple rule: The sum of all exterior angles on a regular polygon is equal to 360[math]^\circ[/math][br][br]Another simple rule:[br][math]\frac{360^\circ}{n}=[/math] the measure of 1 exterior angle (where n = the number of sides in a regular polygon.[br][i]or[br][math]\frac{360^\circ}{exterior\underscore angle}=[/math][/i] n (where n = the number of sides in a regular polygon.