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Basic Trigonometry

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    Find the radius 'r'(?) of the circle 'C' in the attachment.

    I know AO = OB = 6cm

    Where the circle touches the circumference is pi/2 (90deg).

    AOC = pi/6 = (30deg).

    I have no idea what to do to find r. I am unable to use the sin/cosine rules as I don't have enough information..

    Can anyone give me any pointers?
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    (Original post by Joshmeid)
    Click image for larger version. 

Name:	Untitled.png 
Views:	95 
Size:	12.5 KB 
ID:	140937

    Find the radius 'r'(?) of the circle 'C' in the attachment.

    I know AO = OB = 6cm

    Where the circle touches the circumference is pi/2 (90deg).

    AOC = pi/6 = (30deg).

    I have no idea what to do to find r. I am unable to use the sin/cosine rules as I don't have enough information..

    Can anyone give me any pointers?
    Is this not one of the most talked about C2 questions in recent years?

    Anyway extend OC to the arc AB. Can you now determine a if I say that |OC|+a=6. Simple trig from there
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    (Original post by Joshmeid)
    Click image for larger version. 

Name:	Untitled.png 
Views:	95 
Size:	12.5 KB 
ID:	140937

    Find the radius 'r'(?) of the circle 'C' in the attachment.

    I know AO = OB = 6cm

    Where the circle touches the circumference is pi/2 (90deg).

    AOC = pi/6 = (30deg).

    I have no idea what to do to find r. I am unable to use the sin/cosine rules as I don't have enough information..

    Can anyone give me any pointers?
    See the diagram below:



    Use sin in the blue triangle and you are done.

    Spoiler:
    Show

     \displaystyle sin\frac{\pi}{6}=\frac{r}{6-r}

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    (Original post by TheMagicMan)
    Anyway extend OC to the arc AB. Can you now determine a if I say that |OC|+a=6. Simple trig from there
    |OC|+a=6

    a = 6-|OC|

    a = radius

    OC/Sin(pi/2) = a/Sin(pi/6)

    OC/Sin(pi/2) = 6 - |OC|/Sin(pi/6)

    Sin(pi/6)|OC|/Sin(pi/2) = 6 - |OC|

    1/2|OC| = 6 - |OC|

    |OC| = 12 - 2|OC|

    3|OC| = 12

    |OC| = 4

    ___________

    a = 6 - |OC|

    a = 6 - 4

    a = 2

    Therefore Radius = 2. Is this correct?
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    (Original post by Joshmeid)
    |OC| + a = 6

    a = 6 - |OC|

    a = radius

    OC/Sin(pi/2) = a/Sin(pi/6)

    OC/Sin(pi/2) = 6 - |OC|/Sin(pi/6)

    Sin(pi/6)|OC|/Sin(pi/2) = 6 - |OC|

    1/2|OC| = 6 - |OC|

    |OC| = 12 - 2|OC|

    3|OC| = 12

    |OC| = 4

    ___________

    a = 6 - |OC|

    a = 6 - 4

    a = 2

    Therefore Radius = 2. Is this correct?
    I believe so.
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    (Original post by TheMagicMan)
    Is this not one of the most talked about C2 questions in recent years?
    Yes, it is.

    It came in the june 2011 edexcel C2 paper, and this question cost me 100 that day. Though its a simple question but that day the exam conditions also played its part, and i failed to find the radius.
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    (Original post by Joshmeid)
    |OC| + a = 6

    a = 6 - |OC|

    a = radius

    OC/Sin(pi/2) = a/Sin(pi/6)

    OC/Sin(pi/2) = 6 - |OC|/Sin(pi/6)

    Sin(pi/6)|OC|/Sin(pi/2) = 6 - |OC|

    1/2|OC| = 6 - |OC|

    |OC| = 12 - 2|OC|

    3|OC| = 12

    |OC| = 4

    ___________

    a = 6 - |OC|

    a = 6 - 4

    a = 2

    Therefore Radius = 2. Is this correct?
    Yes, it is correct, but the working is too long, see the method i have done in the spoiler.
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    (Original post by raheem94)
    See the diagram below:
    [/spoiler]
    Wow I feel like such a fool looking at that now lol.

    Thanks for the help all.
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    (Original post by raheem94)
    Yes, it is.

    It came in the june 2011 edexcel C2 paper, and this question cost me 100 that day. Though its a simple question but that day the exam conditions also played its part, and i failed to find the radius.
    I sat this paper, and used a reasonably complicated argument involving incircles and inversion...the examiner was undoubtedly not happy...when I saw the approved solution later I was
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    (Original post by TheMagicMan)
    I sat this paper, and used a reasonably complicated argument involving incircles and inversion...the examiner was undoubtedly not happy...when I saw the approved solution later I was
    The ones who sat this paper won't forget this question, like me.

    You would have probably got 100 in it, right?

    Which other modules do you do?
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    (Original post by raheem94)
    The ones who sat this paper won't forget this question, like me.

    You would have probably got 100 in it, right?

    Which other modules do you do?
    I did not get 100, as I was marked down on this question, despite the fact I used a perfectly valid method...it was too late for a remark :rolleyes:

    I do C1-4. FP1-3, S1-3, M1-3 examined, and I've studied M4-5 for interest's sakes
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    (Original post by raheem94)
    It came in the june 2011 edexcel C2 paper, and this question cost me 100 that day. Though its a simple question but that day the exam conditions also played its part, and i failed to find the radius.
    I hate the exam conditions.. Always costing easy marks..
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    (Original post by TheMagicMan)
    I did not get 100, as I was marked down on this question, despite the fact I used a perfectly valid method...it was too late for a remark :rolleyes:

    I do C1-4. FP1-3, S1-3, M1-3 examined, and I've studied M4-5 for interest's sakes
    I have done C1-4, FP1 and M1-3. Will be taking FP2-3, S1-2 in june along with AEA.

    How do you find S1?
    I am doing it nowadays, and hating it. Its completely illogical, right?

    Did you took M3 in jan 2012?
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    (Original post by Joshmeid)
    I hate the exam conditions.. Always costing easy marks..
    Actually that day i was more prepared for chemistry rather than maths, so i couldn't solve challenging questions.

    Exam conditions don't always cost me marks, though they can cost me around 3 marks at times.
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    (Original post by raheem94)
    I have done C1-4, FP1 and M1-3. Will be taking FP2-3, S1-2 in june along with AEA.

    How do you find S1?
    I am doing it nowadays, and hating it. Its completely illogical, right?

    Did you took M3 in jan 2012?
    I hated S1 as well-I think everyone does. I'm taking M3 in June.
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    (Original post by TheMagicMan)
    I hated S1 as well-I think everyone does. I'm taking M3 in June.
    By the way, do you find a lot of difference in S1 methods between different boards?

    I think all boards do it differently.

    How is S2?
    How much time does it takes to prepare, is it more logical?

    How is FP3?

    I am yet to prepare FP3, S2 while S1 is only half done.

    Do you do physics with edexcel?
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    (Original post by TheMagicMan)
    Is this not one of the most talked about C2 questions in recent years?

    Anyway extend OC to the arc AB. Can you now determine a if I say that |OC|+a=6. Simple trig from there
    yh this was the paper that i sat in june

    got 74 for it, was my worst one :emo:
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    (Original post by raheem94)
    By the way, do you find a lot of difference in S1 methods between different boards?
    No idea


    (Original post by raheem94)
    How is S2?
    Not much better

    (Original post by raheem94)
    How much time does it takes to prepare, is it more logical?

    It's just as easy as S1, but there's no justification for why you do anything.

    (Original post by raheem94)
    How is FP3?
    It's the most interesting of any of the maths modules

    (Original post by raheem94)
    Do you do physics with edexcel?

    No WJEC.
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    (Original post by TheMagicMan)
    ...
    Thanks
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    (Original post by raheem94)
    Thanks
    Anyone doing MEI here? Heard you can get 3.5 maths A-Levels. Is that true?

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