I think it would be good if Maxima automatically returned a
rectangular form for complex number multiplication and division; to
get the rectangular form, we need to use expand (products) or rectform
(quotients or products)
(%i1) (1 + %i)*(2/3-%i * 5.70b0);
(%o1) (%i+1)*(2/3-5.7b0*%i)
(%i2) expand(%);
(%o2) 6.366666666666667b0-5.033333333333333b0*%i
Another option is rat + keepfloat, but keepfloat converts big floats
to rationals.
Barton