= Solution
The <streamlines> are the level curves of the <streamfunction>, so $\theta$ is constant: \b[radial rays directed outwards from the origin]. Their arrows point outwards because $Q>0$. A complete straight line through the origin comprises two distinct rays separated by the excluded <line source>. Equivalently, $r\dot\theta=u_\theta=0$ and $\dot r=Q/(2\pi r)>0$ along each <pathline>; the <steady flow> makes these the same curves as the <streamlines>.
\Image[/past-exam-of-the-fluids-and-waves-course-of-the-university-of-oxford/2017-source-streamlines.png]
{title=Radial streamlines of a positive line source}
{description=The excluded source is marked at the origin. Every streamline is an outward ray, and every enclosing circle carries the same outward volume flux $Q$.}
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