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Math Help - Help please! thnk u

  1. #1
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    Help please! thnk u

    I have being doing an old maths test paper to practise and i have done most of it but i am struggling with these last few Q's and i just cnt figure then out! its stressing me out! lol Any help will be much appricated thnx

    1) I need to make C the subject of this formula... P= C
    _____
    C+4

    2) We have practised doing algebracic long division, and from x^3+3x+k divided by x-1,it has a reminder of 6. But from this how can i find k?

    3)finally, a circle intersepts the line with equation x+y=3 at 2 points, A and B. How can i algebraically find the coordinates of A and B.

    and also show that the distance AB is squareroot 162

    Thank you!! to everyone that helps!
    Last edited by Chez_; December 10th 2007 at 08:50 AM. Reason: 3) the circles equation is x^2+y^2= 45
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  2. #2
    Bar0n janvdl's Avatar
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    Quote Originally Posted by Chez_ View Post
    2) We have practised doing algebracic long division, and from x^3+3x+k divided by x-1,it has a reminder of 6. But from this how can i find k?
    f(x) = x^3 + 3x + k

    f(1) = 6

    f(1) = 1^3 + 3(1) + k

    1 + 3 + k = 6

    k = 6 - 4 = 2

    Easy as pie
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  3. #3
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Chez_ View Post
    1) I need to make C the subject of this formula... P= C
    _____
    C+4
    P = \frac{C}{C + 4}

    P(C + 4) = C

    PC + 4P = C

    PC - C = -4P

    (P - 1)C = -4P

    C = -\frac{4P}{P - 1}

    -Dan
    Last edited by topsquark; December 10th 2007 at 09:01 AM.
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    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Chez_ View Post
    3)finally, a circle intersepts the line with equation x+y=3 at 2 points, A and B. How can i algebraically find the coordinates of A and B.

    and also show that the distance AB is squareroot 162
    We need more information about the circle. Do you have the circle's equation, or do you have the center and radius of the circle?

    -Dan
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  5. #5
    Bar0n janvdl's Avatar
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    Quote Originally Posted by Chez_ View Post
    I have being doing an old maths test paper to practise and i have done most of it but i am struggling with these last few Q's and i just cnt figure then out! its stressing me out! lol Any help will be much appricated thnx

    1) I need to make C the subject of this formula... P= C
    _____
    C+4
    P(C + 4) = C

    PC + 4P = C

    4P = C - CP

    4P = C(1 - P)

    \frac{4P}{1 - P} = C


    Quote Originally Posted by Chez_ View Post

    3)finally, a circle intersepts the line with equation x+y=3 at 2 points, A and B. How can i algebraically find the coordinates of A and B.

    and also show that the distance AB is squareroot 162
    Okay, you said the equation is: x^2 + y^2 = 45

    And we are told that y = -x + 3

    x^2 + (-x + 3)^2 = 45

    x^2 + (x^2 - 6x + 9) = 45

    2 x^2 - 6x - 36 = 0

    x^2 - 3x - 18 = 0

    (x - 6)(x + 3) = 0

    So x = 6 or x = -3

    Set those values back into the circle's equation to find the corresponding y-values.
    When you have those, use the distance formula to find the length of AB.
    Last edited by janvdl; December 10th 2007 at 09:06 AM.
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  6. #6
    Bar0n janvdl's Avatar
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    Quote Originally Posted by topsquark View Post
    P = \frac{C}{C + 4}

    P(C + 4) = C

    PC + 4P = C

    **
    PC - C = 4P
    **

    (P - 1)C = 4P

    C = \frac{4P}{P - 1}

    -Dan
    Topsquark, shouldn't that be a -4P ? (Between the asterisks i put in the quote)
    Last edited by janvdl; December 10th 2007 at 09:12 AM. Reason: Grammar error
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  7. #7
    Bar0n janvdl's Avatar
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    Chez, i edited my post above to finish the circle problem.
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