\includegraphics{figure_1}

A table top, in the shape of a parallelogram, is made from two types of wood. The design is shown in Fig. 1. The area inside the ellipse is made from one type of wood, and the surrounding area is made from a second type of wood.

The ellipse has parametric equations,
$$x = 5 \cos \theta, \quad y = 4 \sin \theta, \quad 0 \leq \theta < 2\pi$$

The parallelogram consists of four line segments, which are tangents to the ellipse at the points where $\theta = \alpha$, $\theta = -\alpha$, $\theta = \pi - \alpha$, $\theta = -\pi + \alpha$.

\begin{enumerate}[label=(\alph*)]
\item Find an equation of the tangent to the ellipse at $(5 \cos \alpha, 4 \sin \alpha)$, and show that it can be written in the form
$$5y \sin \alpha + 4x \cos \alpha = 20.$$ [4]

\item Find by integration the area enclosed by the ellipse. [4]

\item Hence show that the area enclosed between the ellipse and the parallelogram is
$$\frac{80}{\sin 2\alpha} - 20\pi.$$ [4]

\item Given that $0 < \alpha < \frac{\pi}{4}$, find the value of $\alpha$ for which the areas of two types of wood are equal. [3]
\end{enumerate}

\hfill \mbox{\textit{Edexcel C4  Q15 [15]}}