imaginary numbers

Some background:  i² = -1     i⁴ = 1     i⁸ = (i⁴) · (i⁴)  = 1 · 1 = 1

 

8 · (i^-6) 

Multiply by  i⁸  (which is just 1):  8 · (i^-6) · i⁸  =  8 · i²  =  8 · -1  =  -8