The sum of the measures of all exterior angle in a polygon with n sides is always [tex] 360^{\circ} [/tex].
Nonagon is a polygon with 9 sides. If this nonagon is regular or equiangular, then all interior angle are congruent, and therefore all exterior angles are congruent. Then the measure of each exterior angle is [tex] \dfrac{360^{\circ}}{9} =40^{\circ} [/tex].
