Circle Property - PS

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by Anurag@Gurome » Tue Dec 06, 2011 1:21 am
karthikpandian19 wrote:In the circle shown in the picture, the radius is 6 and chord AB = 6. What is the area of the shaded region?

(refer the image for other details)
Image
Image

Area of the shaded region = Area of the sector - Area of the triangle OAB
OAB is an equilateral triangle, as all sides are equal. So, each of the angles will be 60 degrees each.
Area of sector = (1/2) * angle subtended at the center of circle * (pi)/180 * r² = (1/2) * 60 * (pi)/180 * 6² = 6(pi)

Length of perpendicular from vertex O to the base AB = √(6)² - (3)² = √27 = 3√3
Area of triangle OAB = (1/2) * 6 * 3√3 = 9√3

Therefore, area of shaded region = 6(pi) - 9√3

The correct answer is E.
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by batmannavneet » Thu Dec 08, 2011 9:52 am
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by karthikpandian19 » Thu Dec 08, 2011 4:48 pm
Anurag,

Can you again explain me the Calculation for the area of the SECTOR??
Anurag@Gurome wrote:
karthikpandian19 wrote:In the circle shown in the picture, the radius is 6 and chord AB = 6. What is the area of the shaded region?

(refer the image for other details)
Image
Image

Area of the shaded region = Area of the sector - Area of the triangle OAB
OAB is an equilateral triangle, as all sides are equal. So, each of the angles will be 60 degrees each.
Area of sector = (1/2) * angle subtended at the center of circle * (pi)/180 * r² = (1/2) * 60 * (pi)/180 * 6² = 6(pi)

Length of perpendicular from vertex O to the base AB = √(6)² - (3)² = √27 = 3√3
Area of triangle OAB = (1/2) * 6 * 3√3 = 9√3

Therefore, area of shaded region = 6(pi) - 9√3

The correct answer is E.

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by Anurag@Gurome » Thu Dec 08, 2011 7:37 pm
Anurag,

Can you again explain me the Calculation for the area of the SECTOR??
A circle has an angle of 360 degrees or 2(pi), and its area = (pi)r²
Hence, a sector with an angle of A degrees, should have an area of [A/2(pi)] * (pi)r² = (A/2) * r²

Image
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