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Math Help - problem with circle

  1. #1
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    problem with circle

    Write an equation for the circle with the given properties.


    38. Center at (1,7), the y-axis is tangent to the circle.

    i don't understand this problem
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  2. #2
    MHF Contributor
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    You should have a standard strucutre for a circle.

    (x-h)^2 + (y-k)^2 = r^2

    (h,k) is the center of the circle.
    r is the radius of the circle

    In this case, you are given the center, (1,7).

    This gives (x-1)^2 + (y-7)^2 = r^2

    You are given a hint to find the radius. If the circle is tangent to the y-axis, there is only one way to do that. The point (0,7) must lie on the circle. This makes the radius 1.

    This gives (x-1)^2 + (y-7)^2 = 1^2

    Done.

    Note: It is important that it is TANGENT to the y-axis. If it said only that it intersected the y-axis, there would be possibly two points of intersection. With a tangent, there is only one such point.
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