The following appears to give two different answers.

Any suggestions?

> restart:
> Re(z);
> Re(a);
> Re(b);
> assume(a>0,b>0,z>0);
> H:=sqrt(b*(1+z)^3+a);
> bot:=int(1/H,z=0..infinity);
> evalf(subs(a=3/4,b=1/4,bot));
> H1:=sqrt((1/4)*(1+z)^3+3/4);
> int(1/H1,z=0..infinity);
> evalf(%);