Decagon is a a plane figure (polygon) with 10 (ten) straight sides and angles. The exterior angle of a regular decagon is= 36°. The interior angle of the regular decagon is 180° - 36° = 144°.
A decagon has 10 sides and angles.
A REGULAR decagon has 10 CONGRUENT sides and angles.
One of its CONGRUENT exterior angles:
One of its CONGRUENT interior angles: