Danny.L
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A sector of a circle of radius 18.0 cm has arc length 43.2 cm.
(i) Find in radians the angle of the sector.
[2](ii) Find this angle in degrees, giving your answer to the nearest degree.
I understand i) as it is r * sin theta = arc length, so sin theta = 43.2/18 = 2/4
ii) I am not so sure on. It is in radians so we need to convert using 180/2.4, right? which gives me 75 degrees, however it comes to 137 as the answer, could someone explain?
I have taught myself radians so forgive me if I have missed something elementary.
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poorform
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For 1. Use s=r \theta. where s is arc length, r is radius and theta is angle in rads.

ii) \pi ~ rads = 180 degrees use that to find your angle.
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corey7695
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(Original post by Danny.L)
A sector of a circle of radius 18.0 cm has arc length 43.2 cm.
(i) Find in radians the angle of the sector.
[2](ii) Find this angle in degrees, giving your answer to the nearest degree.
I understand i) as it is r * sin theta = arc length, so sin theta = 43.2/18 = 2/4
ii) I am not so sure on. It is in radians so we need to convert using 180/2.4, right? which gives me 75 degrees, however it comes to 137 as the answer, could someone explain?
I have taught myself radians so forgive me if I have missed something elementary.
The answer to (i) is using the equation r*theta=arc length, and rearranging to give r/arc length=theta, which is 2.4 radians. To convert to degrees its 2.4*(180/pi) which is 137.5, i believe
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ChoccyPhilly
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I thought r x theta equals arc length?
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poorform
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(Original post by corey7695)
The answer to (i) is using the equation r*theta=arc length, and rearranging to give r/arc length=theta, which is 2.4 radians. To convert to degrees its 2.4*(180/pi) which is 137.5, i believe
don't give full solutions.
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corey7695
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(Original post by poorform)
don't give full solutions.
Sorry, but he now knows where he went wrong, I don't see the issue
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poorform
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(Original post by corey7695)
Sorry, but he now knows where he went wrong, I don't see the issue
1) it's against the rules.

2) if you always read solutions and never do the questions yourself you will never learn the maths. he isn't going to have you feeding him solutions in the exam now is he.
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corey7695
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(Original post by poorform)
1) it's against the rules.

2) if you always read solutions and never do the questions yourself you will never learn the maths. he isn't going to have you feeding him solutions in the exam now is he.
Ok, again, I'm sorry, I'm new to this and I didn't know of any rules, but thanks for being so kind about it.
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Danny.L
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(Original post by corey7695)
Ok, again, I'm sorry, I'm new to this and I didn't know of any rules, but thanks for being so kind about it.
Actually I found this very helpful.
I see where I went wrong.
I did 180/2.4 opposed to (180/pi) *2.4
Often I find it so much easier when someone gives me the answer and then I can try to see where I have gone wrong/the correct method. It's a much more direct and easy way to learn.
When people try to explain without giving the answer it often isnt explained particularly well.
Don't understand why it is against rules tbh, it isnt anything counting towards my a levels, just revision tbh.
thanks!
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