\begin{tikzpicture} \tkzDefPoint(0,5){A}\tkzDefPoint(5,4){B} \tkzDefPoint(0,0){C}\tkzDefPoint(5,1){D} \pgfinterruptboundingbox \tkzInterLL(A,B)(C,D)\tkzGetPoint{I} \endpgfinterruptboundingbox \tkzClipBB \tkzDrawCircle(I,B) \tkzDrawSegments(A,B C,D A,C) \end{tikzpicture}