$\begin{array}{l}\left\{ \begin{array}{l}2r^2  = (x + r)^2  \\ x + 2r = 1 \\ \end{array} \right. \\ \left\{ \begin{array}{l} 2r^2  = (x + r)^2  \\ x = 1 - 2r \\ \end{array} \right. \\ \left\{ \begin{array}{l} 2r^2  = (1 - 2r + r)^2  \\ x = 1 - 2r \\ \end{array} \right. \\ \left\{ \begin{array}{l} 2r^2  = (1 - r)^2  \\ x = 1 - 2r \\ \end{array} \right. \\ \left\{ \begin{array}{l} 2r^2  = 1 - 2r + r^2  \\ x = 1 - 2r \\ \end{array} \right. \\ \left\{ \begin{array}{l} r^2  + 2r - 1 = 0 \\ x = 1 - 2r \\ \end{array} \right. \\ \left\{ \begin{array}{l} r =  - 1 + \sqrt 2  \\ x = 3 - 2\sqrt 2  \\ \end{array} \right. \vee \left\{ \begin{array}{l} r =  - 1 - \sqrt 2  \\ x = 3 + 2\sqrt 2  \\ \end{array} \right.(v.n.) \\ \end{array}$

De straal van de kleine cirkel is gelijk aan $
 - 1 + \sqrt 2
$