(i) Between (-2) and (8)

[ G=\pm\sqrt{(-2)\cdot8}=\pm\sqrt{-16}=\pm4i ]

(Complex G.M.; real G.M. does not exist for opposite signs.)

(ii) Between (-2i) and (8i)

[ G=\pm\sqrt{(-2i)(8i)}=\pm\sqrt{-16 i^2}=\pm\sqrt{16}=\pm4 ]

(iii) Between 6 and 9

[ G=\sqrt{54}=3\sqrt{6} ]

Answers: (i) (\pm4i) (ii) (\pm4) (iii) (3\sqrt{6})