Image of Möbius transformation

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What's the image of the first quadrant $Rez\ge0$ and $Imz\ge0$ under transformation $f(z)=(i-z)/(i+z)$? I know that real axis is mapped to the unit circle, $f(0+i*0)=1$ and $f(\infty)=-1 $.

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Set $w=f(z)$, and rearrange to make $z$ the subject of the formula. In your rearranged form for $z$, write $w=u+iv$. Multiply top and bottom of the fraction by the conjugate of the denominator so that you can identify the real and imaginary parts of $z$ in terms of $u$ and $v$. Now you can apply the inequality conditions given in the question, giving you inequalities for $u$ and $v$. You will end up with a region in the complex plane.