\begin{definition}[Definition:Inclination/Straight Line to Plane]
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Let $P$ be a plane.
Let $L$ be a straight line which intersects $P$ at the point $A$.
Let $Q$ be the perpendicular from a point $B$ on $L$.
Let $C$ be the point where $Q$ intersects $P$.
The '''inclination of $L$ to $P$''' is defined as the angle $BAC$.
In the above diagram, this has been marked as $\theta$.
{{EuclidDefinition|book = XI|def = 5|name = Inclination of Straight Line}}
\end{definition}