Solution (source code)

= Solution

The <plane equation> in normal form is
$$
\boxed{\mathbf n\cdot\mathbf r=1,\qquad\text{equivalently}\qquad \frac xa+\frac yb+\frac zc=1.}
$$
An equivalent vector parametrization is $\mathbf r=\mathbf a+s(\mathbf b-\mathbf a)+t(\mathbf c-\mathbf a)$, with $s,t\in\mathbb R$.