- #1
Zeeree
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Homework Statement
Find the images of the following region in the z-plane onto the w-plane under the linear fractional transformations
The first quadrant ##x > 0, y > 0## where ##T(z) = \frac { z -i } { z + i }##
Homework Equations
The Attempt at a Solution
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So for this, I looked at the poles of ##T(z)## first and found that ##z = -i## does not lie on the lines that bound the first quadrant i.e ## x = 0 ## and ## y = 0 ##. Since the image of a line is either a line or a circle, I deduced that the image is a circle since the singularity does not lie on the lines.
Upon substituting ## z = 0 ## and ## z = 1 ## where both are points on the bounding lines, I obtained ## T(0) = -1 ## and ## T(1) = -i ## leading me to believe that it in fact the unit circle (Exterior or interior can be found out later)
However, because it's a mapping of only the FIRST quadrant, intuitively I think the image is the semi-circle but I'm unsure how to show this. If I were to substitute ## z = -1 ## into T(z), I obtain ## T(z) = i ## which gives me the hunch that it's the upper half unit circle (since ## z = -1 ## is not in the first quadrant. I don't think this is enough.