\begin{definition}[Definition:Perpendicular Distance]
Let $\LL$ be a straight line.
Let $P$ be a point not on $\LL$.
Let a perpendicular be dropped from $P$ to $\LL$, intersecting $\LL$ at $A$.
The '''perpendicular distance''' from $P$ to $\LL$ is defined as being the length of the line $AP$.
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\end{definition}