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What is the area of a regular dodecagon with a side length of 9 centimeters? Round your answer to the nearest tenth.

 Apr 1, 2020
 #1
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Formula: (A_dodecagon=3(2+√3)•s^2)

 

Plug in the values now!

 Apr 1, 2020
 #3
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It's better to understand how to find the area of regular polygons: 1/2 * a * p, where a stands for the apothem and p stands for the perimeter of the polygon...

 

Mark the center and create a triangle joining two of the vertices. From the center of the polygon, drop a perpendicular line(this is the apothem !)

 

The central angle is 360 / number of sides, so 360/12=30.

 

Since the perpendicular line cuts the angle of 30 degrees in half, we have two fifteen(15) degree angles..

 

By the Law of Sines, we have \(\frac{sin 15}{4.5}=\frac{sin 75}{y}\). Solving for \(y\), gives the apothem, which is approximately 16.794 centimeters.

 

The perimeter of the polygon is 9 * 12 =108 centimeters.

 

Thus, the answer is \(\frac{1}{2}*16.794*108\approx906.9\) centimeters squared.

 Apr 1, 2020

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