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Help with math problem please, +++++++karma

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Drew.C
Posts: 1757 - Karma: 39

th circle below has the center o and a radius of lenght 5. if the area of the shaded reigon is 20 pie, what is the value of x.

a: 18

b: 36

c: 45

d: 54

e: 72

Click for larger image

Dec 14 2008 7:04PM
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Drew.C
Posts: 1757 - Karma: 39
i also need an explanation
Dec 14 2008 7:10PM
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bout_it
Posts: 1233 - Karma: 17
that's tough..what class is this? trigenometry?
Dec 14 2008 7:11PM
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crunkasfuck
Posts: 752 - Karma: 352
B
Dec 14 2008 7:13PM
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ClownPrince
Posts: 500 - Karma: 10
A (18)

If the shaded region's area is 20pi, the area of the non-shaded region is 5pi (total area 25pi - pi*r^2). That means the angle besides x and the right angle (we'll call it y) is 1/5 of 360 degrees, or 72 degrees (because the area of the non-shaded region is 1/5 the total area). Since x, y, and right angle must add up to 180 degrees (because it's a triangle) x must be 180 - (72+90), or 18.
Dec 14 2008 7:15PM
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Rusty10
Posts: 4 - Karma: 10
Well the area of a circle is (pie)(r)(r).

Area of the total circle = (pie)(5)(5) = 25(pie)

If you think of the circle as 5 equal wedges, then one wedge ( which is what the triangle represents) is equal to 360/5 degrees which is = to 72 degrees.

Now that you know the angle of the lower left angle of the triangle, you can find the angle at x. 360-72-90 = 18 degrees.

So your answer is: a: 18.



Dec 14 2008 7:23PM
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Rusty10
Posts: 4 - Karma: 10
damn beat me to it.
Dec 14 2008 7:23PM
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Drew.C
Posts: 1757 - Karma: 39
hey guys thanks so much ++++ k. you saved my life hahaha
Dec 14 2008 7:38PM
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CFD
Posts: 1009 - Karma: 197
i think you meant 180 - 72 - 90 = 18
Dec 14 2008 7:49PM
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