negative poly-exponents

[Alexander Bluem]

hello,

I am trying to design discrete filters using the z-transform.
At my university we are doing so in this form:

H(z) = ( (z - z_01) * (z - z_02) ) / ( (z - z_x1) * (z - z_x2) )

of course the result is with positive z-exponents. now: how do I get the 
representation with negative exponents ?

for example:

zo=1.25;
zx=0.8;
z=poly(0,'z');

(z-zo)/(z-zx)
ans =
   - 1.25 + z
     --------
   - 0.8 + z

but I'd like this output:
            -1
   1 - 1.25z
   --------
           -1
   1 - 0.8z


any hints are much appreciated.

Alex