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Math Help - Circles

  1. #1
    Junior Member Misa-Campo's Avatar
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    Circles

    Let A and B be the points of (-1,0) and (2,0) respectively and let P be the variable point (x,y).

    i) write down expressions for PA and PB in terms of x and y

    ii) suppose that P moves such that PA=2PB. Deduce that P moves on a circle

    iii) Hence find the center and radius of this circle
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  2. #2
    Moo
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    Hello,

    Quote Originally Posted by Misa-Campo View Post
    Let A and B be the points of (-1,0) and (2,0) respectively and let P be the variable point (x,y).

    i) write down expressions for PA and PB in terms of x and y
    You should know the formula for a distance between 2 points :
    M(a,b) N(c,d)
    Then

    Then for example

    ii) suppose that P moves such that PA=2PB. Deduce that P moves on a circle
    Square the equality PA=2PB it's far easier to work on this than the square roots that PA and PB represent.

    if you can't find the solution, tell me what you've done and we'll work it out ^^

    iii) Hence find the center and radius of this circle
    Equation of a circle, of radius R and center O(m,n) :
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  3. #3
    Junior Member Misa-Campo's Avatar
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    Thanks

    Quote Originally Posted by Moo View Post
    Hello,


    You should know the formula for a distance between 2 points :
    M(a,b) N(c,d)
    Then

    Then for example


    Square the equality PA=2PB it's far easier to work on this than the square roots that PA and PB represent.

    if you can't find the solution, tell me what you've done and we'll work it out ^^


    Equation of a circle, of radius R and center O(m,n) :
    Thanks, im kinda get it now but still stuck on the mid question, heres what i got:


    dunno what to do after that
    Last edited by Misa-Campo; July 24th 2008 at 06:54 PM.
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  4. #4
    Moo
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    That's a good start !

    Divide the equation by 3 and see if you can complete squares
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  5. #5
    Junior Member Misa-Campo's Avatar
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    ohhhhhh i see
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