z^3 = (8i-16) / (2i+1)

LS = (x+yi)^3 = (x+yi)(x+yi)(x+yi)
   = ( x^2 + 2xyi + (y^2)(i^2) )(x+yi)
   = x^3 + 2(x^2)yi + x(y^2)(i^2)
   + (x^2)yi + 2x(y^2)(i^2) + (y^3)(i^3)
   = x^3 + 3(x^2)yi - 3x(y^2) - (y^3)i

     (8i-16) * (2i-1)   -40i
PS = ---------------- = ---- = 8i
     (2i+1)  * (2i-1)   -5

x^3 + 3(x^2)yi - 3x(y^2) - (y^3)i  =  8i

/ x^3 - 3x(y^2) = 0
\ 3(x^2)y - (y^3) = 8