The dihedral group D5 consists of reflections around the red symmetry lines of the white regular pentagon and of rotations by angles 2pi/5. That is the angle between the white and the yellow vector must be m*2pi/5 (m=1,2,3,4,5) in order to give a symmetry rotation of the group. You can drag the yellow vector interactively.
Soli Deo Gloria. Created with Cinderella by Eckhard Hitzer (Fukui).