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prep question

by jc114 » Tue Apr 17, 2007 2:24 am
There is an equilateral triangle- the length of each side is 10. There is a circle inscribed inside the triangle- what is its area?

A. 3(pi)/5
b. 20pi/3
C. 25pi/3
D. 3pi/25
E. 9 pi

The answer is C but i keep getting a different radius. :oops:
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by Cybermusings » Tue Apr 17, 2007 4:32 am
For an equilateral triangle always remember that the Area of the Incircle = 1/12*pie*(a^2)
Likewise for an equilateral triangle the Area of the Circumcircle = 1/3*pie*(a^2); Where a is the side of the triangle.
Hence in this case the area would be 1/12*pie*10^2
=25pie/3
Do you want additional help with the formula?
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by jc114 » Wed Apr 18, 2007 3:40 pm
no i got it..i just made a dumb error..thanks!
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by Tame the CAT » Sun May 06, 2007 6:16 pm
Cybermusings wrote:For an equilateral triangle always remember that the Area of the Incircle = 1/12*pie*(a^2)
Likewise for an equilateral triangle the Area of the Circumcircle = 1/3*pie*(a^2); Where a is the side of the triangle.
Hence in this case the area would be 1/12*pie*10^2
=25pie/3
Do you want additional help with the formula?
WOW! I didn't know this.

Thanks for the insight!
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