By calculating the angle between the line AB and the normal to the plane of the layer, find the angle at which the pipeline cuts through the layer.
8 Part of the track of a roller-coaster is modelled by a curve with the parametric equations
$$x = 2 \theta - \sin \theta , \quad y = 4 \cos \theta \quad \text { for } 0 \leqslant \theta \leqslant 2 \pi$$
This is shown in Fig. 8. B is a minimum point, and BC is vertical.
\begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{5c149cb5-7392-4219-b285-486f4694aa6f-4_602_1447_488_351}
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\caption{Fig. 8}
\end{figure}