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? asked in Science & MathematicsMathematics · 3 years ago

Find the equation of an osculating circle?

I need help with this question. I have already found k = 1/2, the radius 2, and N = -i -j but I am unsure how to locate the center of the circle

Find an equation for the circle of curvature of the curve r(t) = 2(ln t)i - [t+ (1/t)]j

e^-2 <= t <= e^2, at the point (0,-2) where t = 1

1 Answer

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  • 3 years ago

    The radius from the point of intersection to the center of the circle is perpendicular to the tangent line at the point.

    r'(t) = (2/t)i - [1 - (1/t^2)]j

    r'(1) = 2i

    The direction perpendicular to this is, of course, ±j.

    To find the sign, we use second derivative:

    r"(t) = (-2/t^2)i - (2/t^3)j

    r"(1) = -2i - 2j

    The second derivative is negative, so the curve is concave down.

    The center is at:

    (0, -2 - r)

    (0, -2 - 2)

    (0, -4)

    https://www.desmos.com/calculator/mchkuot8mv

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