- #1
Dromepalin
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Homework Statement
This problem is an already solved one in Marsden and Hoffman's Basic Complex Analysis, but I can't seem to work out the last step.
Here's the problem:
Suppose a,b,c,d are real and ad-bc>0. Then show that [tex] T(z) = \frac{az+b}{cz+d}[/tex] leaves the upper half plane invariant. Show any conformal map of the upper half plane is of this form.
Homework Equations
The Solution to the second half:
Suppose T maps the upper half plane conformally to itself. Then
[tex] W(z) = \frac{T(\frac{1}{i}*\frac{z+1}{z-1})-i}{T(\frac{1}{i}*\frac{z+1}{z-1})+i}[/tex]
is a conformal map of the unit disk to itself. Now W has the form:
[tex]W(z) = e^{i\theta}\frac{z-z_{0}}{1-\overline{z_{0}}z}[/tex]
and so [tex]e^{i\theta}\frac{\frac{w-i}{w+i}-z_{0}}{1-\overline{z_{0}}\frac{w-i}{w+i}} =\frac{T(w)-i}{T(w)+i}[/tex]
Solving for T(w): <=== This is the part I don't understand!
[tex] T(w) =\frac{w*Re[(1-z_{0})e^{i\theta/2}] - Im[(1+z_{0})e^{i\theta/2}]}{w*Im[(1-z_{0})e^{i\theta/2}] + Re[(1+z_{0})e^{i\theta/2}]}[/tex]
The Attempt at a Solution
How on Earth did the author get that value for T(w). I have tried pages of mindless algebraic manipulation to no avail.
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