SOLUTION: area of a regular pentagon inscribed in a circle of radius 12cm.

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Question 3904: area of a regular pentagon inscribed in a circle of radius 12cm.
Answer by khwang(438) About Me  (Show Source):
You can put this solution on YOUR website!
Let AB be a side of the pentagon and O be the center.
then angle AOB = 360/5 = 72 degrees.

And the area of AOB = 1/2 AOsin angle AOB
= 1/2 r^2 sin AOB = 1/2 * 144 sin 72'
= 72 sin 72 = 68.48 cm^2
So the area of the pentagon = 5 area of triangle AOB = 342.38 cm^2
Kenny