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    Q. the circle x^2 + y^2 = 20 intersects the line y = x -2 at the point A and B
    a) work out the coordinates of A and B
    b) work out the length of AB

    (I am stuck on part a :P )
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    Solve a pair of simultaneous equations.

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    Square the equation of the line. Substitute for y^2 in the equation of the circle.
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    For part a) I would input (x-2) into the circle equation to get x^2 + (x-2)^2 = 20 and then solve for x. Then I would just input the values of x into y = x-2 to get y
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    If you simply the equation
    it will be x^2 - 2x - 9 = 0
    correct ?
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    (Original post by aking144)
    If you simply the equation
    it will be 2x^2 - 2x - 9 = 0
    correct ?
    I don't believe so.
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    (Original post by joostan)
    I don't believe so.
    I'm confused
    could some do a trial run ?
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    (Original post by aking144)
    I'm confused
    could some do a trial run ?
    Post what you did, and I will attempt to find where you're going wrong.
    We're not meant to provide solutions unless it is absolutely necessary
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    (Original post by joostan)
    Post what you did, and I will attempt to find where you're going wrong.
    We're not meant to provide solutions unless it is absolutely necessary
    ok

    x^2 + ( x - 2 )^2 = 20
    - 2x^2 - 4x + 2 = 20
    - 2x^2 -4x -18
    - x^2 - 2x - 9 = 0
    thats what i have done so far
    But the answer is an integer
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    (Original post by aking144)
    ok

    x^2 + ( x - 2 )^2 = 20
    =>2x^2 - 4x + 2 = 20
    =>2x^2 -4x -18
    =>x^2 - 2x - 9 = 0
    thats what i have done so far
    But the answer is an integer
    Arrows are better than - signs when saying that something implies something else.
    And what is (-2)2
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    (Original post by joostan)
    Arrows are better than - signs when saying that something implies something else.
    And what is (-2)2
    lol making all the mistakes on the net lol
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    (Original post by aking144)
    ok

    x^2 + ( x - 2 )^2 = 20
    - 2x^2 - 4x + 2 = 20
    - 2x^2 -4x -18
    - x^2 - 2x - 9 = 0
    thats what i have done so far
    But the answer is an integer
    You haven't multiplied it out right, it should come out like this:

    x^2 + (x^2 - 4x + 4) = 20

    2x^2 - 4x + 4 = 20

    2x^2 - 4x - 16 = 0

    You then factorise the equation to get (2x - 8)(x + 2) = 0

    So 2x - 8 = 0 and x + 2 = 0

    2x = 8

    x = 4

    Therefore x = 4 and x = -2

    To find y you just put these two values of x into y = x - 2.
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    (Original post by aking144)
    lol making all the mistakes on the net lol
    No worries - post again if you get any more problems.
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    thanks it really helps
 
 
 
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