Question

prove that the interior angle of a regular Pentagon is three times the exterior angle of regular decagon

Answer 1

Each angle =(n-2)180/n
Each angle of regular pentagon=(5-2)180/5=108°
Since the sum of exterior all exterior angles of a polygon=360°
Therefore each exterior angle of decagon=360/8
=36°
3*36=108°
Hence proved

Answer 2

Each exterior angle of a regular decagon is 360/10 ( no. of sides in a regular decagon is 10)