Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter10: Sequences, Series, And Probability
Section10.5: The Binomial Theorem
Problem 15E
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A regular n-gon is inscribed in a circle of radius r.
(a) Derive a formula for the area of the regular n-gon in terms of n and r.
Use a trigonometric function and radian angle measure.
Hint: A regular n-gon inscribed in a circle of radius r can be partitioned into n isosceles triangles.
An inscribed regular 10-gon (decagon) is shown as an example.

(a)
Transcribed Image Text:(a)
Expert Solution
Step 1

Observe that complete 360 degree angle at the centre of the circle is divided into n parts. Thus to calculate the altitude, consider just one of the triangles of the n-gon as shown:

360
r, radius
n
В
A
CB altitude rsin(360/n)
Step 2

In triangle OCB, OB is the hypotenuse and CB is the perpendicular, thus:

360°
ВС
= sin
ОВ
п
3600
Altitude BC =r sin
п
Step 3

Area of triangle OAB is:

1
-x OA x BC
2
Area of triangle OAB
360°
1
Exrxrsin
2
360°
-sin
2
п
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