Solution
= Solution
The removed <vector> is the <orthogonal projection> of $\mathbf r$ onto the <line> through the origin in direction $\hat{\mathbf n}$. The remaining <vector> measures the perpendicular displacement from that <line>. Fixing its <Euclidean norm> at $2$ therefore describes \b[an infinite circular <cylinder> of radius $2$], with axis $x=z$, $y=0$.