Distance between skew lines
= Distance between skew lines
For lines $\mathbf a_1+\lambda\mathbf u_1$ and $\mathbf a_2+\mu\mathbf u_2$ with $\mathbf u_1\times\mathbf u_2\ne0$, their shortest distance is
$$
\frac{|(\mathbf a_2-\mathbf a_1)\mathbin\cdot(\mathbf u_1\times\mathbf u_2)|}{|\mathbf u_1\times\mathbf u_2|}.
$$