About the conformal map $f$ of a slit disc onto a unit disc with the condition $f(i/2)=0$

complex-analysisconformal-geometry

The slit disc is $D$ \ $(-1,a]$ where a belongs to $(-1,1)$. The question asks me to find a conformal map from this slit disc to the unit disc and such map satisfy $f(i/2) = 0$. I currently have no certain clue how to construct such a map, but I guess I need to start with certain simpler maps and compose them together to make this $f$. So is there any general method or thought to construct such a map?

Best Answer

With $\frac{z-a}{1-az}$ send $D\setminus(-1,a]$ to $D\setminus(-1,0]$,

with $i z^{1/2}$ send $D\setminus(-1,0]$ to $|z|<1,\Im(z)>0$,

with the inverse of $z\to \frac{z-1}{z+1}$ send $|z|<1,\Im(z)>0$, to $\Re(z)>0,\Im(z)>0$,

with $z^2$ send $\Re(z)>0,\Im(z)>0$ to $\Im(z)>0$,

which is biholomorphic to the unit disk with $\frac{z-i}{z+i}$.

Composing with an automorphism of the unit disk you get $f(i/2) = 0$

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