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Math Help - Concentric Circles

  1. #1
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    Concentric Circles

    Two concentric circles have radii 3 and 7 cm. Find, to the nearest hundredth, the length of a chord of the larger circle that is tangent to the smaller circler.

    I tried drawing it out, but could not make the connections. Any help would be greatly appreciated. Also please show steps that way I know how you did them any why you did them.
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  2. #2
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    Quote Originally Posted by BrendanLoftus View Post
    Two concentric circles have radii 3 and 7 cm. Find, to the nearest hundredth, the length of a chord of the larger circle that is tangent to the smaller circler.

    I tried drawing it out, but could not make the connections. Any help would be greatly appreciated. Also please show steps that way I know how you did them any why you did them.
    Is this the answer?
    4\sqrt{10}=12.65
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  3. #3
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    This is how i'm reading it.

    The chord will go from one side of the bigger circle just touching the smaller circle. Plot 2 relations x^2+y^2= 3^2 and x^2+y^2= 7^2 and draw the line, using the relations you should be able to find the length.

    Spoiler:
    2\times \sqrt{49-3^2}
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  4. #4
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    Here is a photo[IMG]file:///C:/Users/Dustin/Desktop/PicturCircles.jpg[/IMG]
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  5. #5
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    Quote Originally Posted by BrendanLoftus View Post
    Two concentric circles have radii 3 and 7 cm. Find, to the nearest hundredth, the length of a chord of the larger circle that is tangent to the smaller circle.

    .
    Let O be the center of the concentric circles. Let AB be the chord which touches the smaller ciecle at D.

    Now AO is the radius of the larger circle.

    OD is the radius of the smaller circle.

    ADO is a right angled triangle.

    So AD^2 = OA^2 - OD^2

    And AB = 2AD.

    Now solve.
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  6. #6
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    thanks so much
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