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Homework Help: Tangent to y axis with center(-3,4) whats the eqn of circle?

  1. Mar 26, 2005 #1
    the center is (-3,4) and tangent to the y-axis

    how will I find the equation of the circle?

    I know what tangent means but at what point? Can someone give me a clue? :rolleyes:
  2. jcsd
  3. Mar 27, 2005 #2

    Math Is Hard

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    I am pretty rusty at this, and I am not sure I understand the wording, but could it simply mean that your circle touches the point (0,4) on the y-axis? I am assuming that the line x = 0 is tangent to the curve.
  4. Mar 27, 2005 #3
    I think the radius is 3

    therefore the equation of the circle is

    [tex] (x+3)^2 + (y-4)^2 = 9 [/tex]

    is this correct?
  5. Mar 27, 2005 #4
    that's fine~
  6. Mar 27, 2005 #5
    how come the radius wasnt 4?
  7. Mar 27, 2005 #6
    the center is at [itex](-3, 4)[/itex] and the circle is tangent to the [itex]y[/itex] axis, which implies that it is tangent at [itex](0, 4)[/itex]. Thus the radius is the distance between [itex](0, 4)[/itex] and [itex](-3, 4)[/itex] which is clearly 3.
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