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Math Help - circle geometry help 4

  1. #1
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    circle geometry help 4

    http://www.boardofstudies.nsw.edu.au...hs_ext1_05.pdf

    with explanation and reasons please question 3d
    Last edited by andy69; May 21st 2010 at 07:02 PM. Reason: forgot to type what question
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  2. #2
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    What do you specifically do not understand?
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  3. #3
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    Quote Originally Posted by spruancejr View Post
    What do you specifically do not understand?
    i have trouble giving the reasons in circle geometry can you or somebody else help me.its just question 3d
    Last edited by andy69; May 21st 2010 at 07:07 PM.
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  4. #4
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    Quote Originally Posted by andy69 View Post
    i have trouble giving the reasons in circle geometry can you or somebody else help me.its just question 3d
    When the two chords Ab and CD intersect each other at E, they satisfy the following condition.

    \frac{AE}{EB} = \frac{CE}{ED} .............(1)

    AE = 4, AB = 7. So EB = ...?

    CD = l, ED = x, so CE = ...?

    Substitute these values in equation (1) and simplify.

    The equation obtained is

    x^2 - lx + 12 = 0. Or

    l = x + \frac{12}{x}

    To get the minimum length of the chord CD, find dl/dx and equate it to zero. Then solve for x. Substitute this value in eq.(1) to find CF, then find CD.
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  5. #5
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    Quote Originally Posted by sa-ri-ga-ma View Post
    When the two chords Ab and CD intersect each other at E, they satisfy the following condition.

    \frac{AE}{EB} = \frac{CE}{ED} .............(1)

    AE = 4, AB = 7. So EB = ...?

    CD = l, ED = x, so CE = ...?

    Substitute these values in equation (1) and simplify.

    The equation obtained is

    x^2 - lx + 12 = 0. Or

    l = x + \frac{12}{x}

    To get the minimum length of the chord CD, find dl/dx and equate it to zero. Then solve for x. Substitute this value in eq.(1) to find CF, then find CD.
    im really sorry about this but im not sure what to do im not very good at circle geometry because my teacher was absent for most of this whole topic and know i have a test about it, again im really sorry can you explain it abit more.
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  6. #6
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    Quote Originally Posted by andy69 View Post
    im really sorry about this but im not sure what to do im not very good at circle geometry because my teacher was absent for most of this whole topic and know i have a test about it, again im really sorry can you explain it abit more.
    Open any text book and find the properties of the circle. For that there is no need of any teacher.
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  7. #7
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    Quote Originally Posted by sa-ri-ga-ma View Post
    When the two chords Ab and CD intersect each other at E, they satisfy the following condition.

    \frac{AE}{EB} = \frac{CE}{ED} .............(1)

    AE = 4, AB = 7. So EB = ...?

    CD = l, ED = x, so CE = ...?

    Substitute these values in equation (1) and simplify.

    The equation obtained is

    x^2 - lx + 12 = 0. Or

    l = x + \frac{12}{x}

    To get the minimum length of the chord CD, find dl/dx and equate it to zero. Then solve for x. Substitute this value in eq.(1) to find CF, then find CD.
    EB=3 how can you get CE when theres 2 unknowns the fraction would just be 4/3=CE/X
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  8. #8
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    Quote Originally Posted by andy69 View Post
    EB=3 how can you get CE when theres 2 unknowns the fraction would just be 4/3=CE/X
    CE = CD - ED = (l - x)
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  9. #9
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    Quote Originally Posted by sa-ri-ga-ma View Post
    CE = CD - ED = (l - x)
    ok so 4/3=(l-x)/x
    cross multiply
    4x=3(l-x)
    4x=3l-3x
    4x+3x=3l
    7x=3l
    x=3l/7

    now do i sub this answer into the 2nd equation that you said
    Last edited by andy69; May 22nd 2010 at 06:40 PM.
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  10. #10
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    Quote Originally Posted by andy69 View Post
    now do i sub this answer into the 2nd equation that you said
    I think it's time you be told that you need classroom help;
    we can't replace your teacher here...
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  11. #11
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    Quote Originally Posted by andy69 View Post
    ok so 4/3=(l-x)/x
    cross multiply
    4x=3(l-x)
    4x=3l-3x
    4x+3x=3l
    7x=3l
    x=3l/7

    now do i sub this answer into the 2nd equation that you said
    Sorry.

    The expression should be

    AE*EB = CE*ED
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  12. #12
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    Quote Originally Posted by sa-ri-ga-ma View Post
    Sorry.

    The expression should be

    AE*EB = CE*ED
    (4)x(3)= x(l - x)
    7=xl-x^2
    x^2+7=xl
    x^2+7/x=l
    so after this i should sub it into any two of those equations?
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  13. #13
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    Quote Originally Posted by andy69 View Post
    (4)x(3)= x(l - x)
    7=xl-x^2
    x^2+7=xl
    x^2+7/x=l
    so after this i should sub it into any two of those equations?
    What is 4X3 ?

    What is 4 + 3 ?
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  14. #14
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    Quote Originally Posted by sa-ri-ga-ma View Post
    What is 4X3 ?

    What is 4 + 3 ?
    * this sign is times isnt it.
    12=xl-x^2
    12+x^2=xl
    12+x^2/x=l sorry i miscalculated.
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  15. #15
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    Quote Originally Posted by andy69 View Post
    * this sign is times isnt it.
    12=xl-x^2
    12+x^2=xl
    12+x^2/x=l sorry i miscalculated.
    12+x^2/x=l

    Write the above equation as

    (12/x) + x = l.
    Find dl/dx and equate it to zero. Then solve for x. You know the relation between x and l. Hence find the minimum length of the chord.
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