Parametric equation of a straight line
= Parametric equation of a straight line
{title2=$r=a+st,\quad s\in\mathbb R$}
= Parametric equations of a straight line
{synonym}
A <straight line> through a point $a$ in nonzero direction $t$ is the set of vectors $r=a+st$ for real parameter $s$. If $|t|=1$, changes in the parameter equal signed distances along the line. Two such lines intersect exactly when their two parameter formulas give a common vector for some choice of their parameters.