  We consider quantum group theory on the Hilbert space level. We find all
solutions for scalar and general exponential equations for the quantum ``az+b''
group. It turns out that there is a simple formula for all of them involving
the quantum exponential function F_N. The very interesting theorem we prove by
the way is the one on the existence of normal extension of certain sum of
normal operators.
  To put it differently, we find all unitary representations of the braided
quantum group related to the quantum ``az+b'' group. This is the most difficult
result needed to classify all unitary representations of the quantum ``az+b''
group. Eventually this enables us to give a formula for all unitary
representations of the quantum ``ax+b'' group in our next paper.
