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Need help with A level C2 maths

  1. Jan 27, 2008 #1
    Hi, i think this is the place for this type of questions? If not, please move it.

    I need help with these type of questions, i am not being able to do them.
    Theyre from Edexcel Pure mathematics C1 and C2.
    Thanks in advance.

    1. The problem statement, all variables and given/known data

    AB is a chord of a circle where A is at (1,3) and B is at (4,4).
    The tangent to the circle at A is the line y= 2x + 1.

    2. Relevant equations

    Find the equation of the circle.

    3. The attempt at a solution

    Well, i did try, but i dont know how to do this stuff.
    I found the gradient of the normal then found the normals equation using
    y - y1 = m(x - x1)
    but cant get any further.
    I think i have to find the centre and teh radius and that will give me the circle's equation, please help.

    Also, i need help with these type of questions:

    The point (6,1) lies on the circle x^2 - y^2 - 8x - 4y + 15 = 0

    Find the coordinates of the second point at which the normal cuts the circle.

    How the hell do you do that? It gives a hint, "draw a sketch"

    Thanks
    =)
     
  2. jcsd
  3. Jan 27, 2008 #2

    rock.freak667

    User Avatar
    Homework Helper

    First one I can think of one way to find it but that may be too tedious to do it out. But it all begins with the general equation of a circle.

    General equation of a circle is:

    [tex]x^2+y^2+2fx+2gy+c=0[/tex]

    Centre=(-f,-g) and radius=[itex]\sqrt{f^2+g^2-c}[/itex]
     
  4. Jan 27, 2008 #3
    Thanks man. that equation helped. its not on the formula sheet of the past papers so ill have to memorise that for tommorows test.

    EDIT: Yah, and i figured out a way to do the second one too.
    Thanks
     
    Last edited: Jan 27, 2008
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