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n.3bhw4vr 8kr tigate the relationship between the number of sides and the area of an enclosure with a given perimeter.
rr.kwvn 8h3b 4A farmer wants to create an enclosure for his chickens, so he has purchased 28 meters of chicken coop wire mesh.
1. Initially the farmer considers making a rectangular enclosure.
1. Complete the following table to show all the possible rectangular enclosures with sides of at least 4 m he can make with the 28 m of mesh. The sides of the enclosure are always a whole number of metres.
2. What is the name of the shape that gives the maximum area?
The farmer wonders what the area will be if instead of a rectangular enclosure he uses an equilateral triangular enclosure.
2. Show that the area of the triangular enclosure will be $\frac{196 \sqrt{3}}{9} $.
Next, the farmer considers what the area will be if the enclosure has the form of a regular pentagon.
The following diagram shows a reqular pentagon.
Let O be the centre of the regular pentagon. The pentagon is divided into five congruent isosceles triangles and angle $A \widehat{O}$ B is equal to $\theta $ radians.
3. 1. Express $\theta$ in terms of $\pi$ .
2. Show that the length of OA is $\frac{14}{5}$$ \operatorname{cosec}\left(\frac{\pi}{5}\right) \mathrm{m}$ .
3. Show that the area of the regular pentagon is $\frac{196}{5} \cot \left(\frac{\pi}{5}\right) \mathrm{m}^{2} $.
Now, the farmer considers the case of a regular hexagon.
4. Using the method in part (c), show that the area of the regular hexagon is
$\frac{196}{6} \cot \left(\frac{\pi}{6}\right) \mathrm{m}^{2}$
The farmer notices that the hexagonal enclosure has a larger area than the pentagonal enclosure. He considers now the general case of an n -sided regular polygon. Let A_{n} be the area of the n -sided regular polygon with perimeter of 28 m .
5. Show that $A_{n}=\frac{196}{n} \cot \left(\frac{\pi}{n}\right)$ .
6. Hence, find the area of an enclosure that is a regular 14-sided polygon with a perimeter of 28 m . Give your answer correct to one decimal place.
7. 1. Evaluate $\lim _{n \rightarrow \infty} A_{n}$
2. Interpret the meaning of the result of part (g) (i).