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Find dy/dx and d2y/dx2 at (1,1) for the equation ((x-h)2)/(a2) + ((y-k)2)/(b2) = 1

Mathematics

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Answer

−b2(1−h)a2(1−k)-\frac{b^2(1-h)}{a^2(1-k)}

−b4a2(1−k)3-\frac{b^4}{a^2(1-k)^3}

Step-by-step solution

7 steps
  1. Differentiate the given equation implicitly with respect to xx.

    The equation is:

    (x−h)2a2+(y−k)2b2=1\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1

    Differentiating both sides with respect to xx:

    2(x−h)a2+2(y−k)b2dydx=0\frac{2(x-h)}{a^2} + \frac{2(y-k)}{b^2} \frac{dy}{dx} = 0
  2. Solve for dydx\frac{dy}{dx}.

    2(y−k)b2dydx=−2(x−h)a2\frac{2(y-k)}{b^2} \frac{dy}{dx} = -\frac{2(x-h)}{a^2} dydx=−2(x−h)a2⋅b22(y−k)\frac{dy}{dx} = -\frac{2(x-h)}{a^2} \cdot \frac{b^2}{2(y-k)} dydx=−b2(x−h)a2(y−k)\frac{dy}{dx} = -\frac{b^2(x-h)}{a^2(y-k)}
  3. Evaluate dydx\frac{dy}{dx} at the point (1,1)(1,1).

    Substitute x=1x=1 and y=1y=1 into the expression for dydx\frac{dy}{dx}:

    dydx∣(1,1)=−b2(1−h)a2(1−k)\frac{dy}{dx} \Big|_{(1,1)} = -\frac{b^2(1-h)}{a^2(1-k)}

    The first derivative at (1,1)(1,1) is −b2(1−h)a2(1−k)\boxed{-\frac{b^2(1-h)}{a^2(1-k)}}.

  4. Differentiate dydx\frac{dy}{dx} with respect to xx to find d2ydx2\frac{d^2y}{dx^2}.

    We have dydx=−b2a2x−hy−k\frac{dy}{dx} = -\frac{b^2}{a^2} \frac{x-h}{y-k}.
    Using the quotient rule ddx(uv)=u′v−uv′v2\frac{d}{dx}\left(\frac{u}{v}\right) = \frac{u'v - uv'}{v^2}, where u=x−hu = x-h and v=y−kv = y-k:
    u′=1u' = 1
    v′=dydxv' = \frac{dy}{dx}

    d2ydx2=−b2a21⋅(y−k)−(x−h)dydx(y−k)2\frac{d^2y}{dx^2} = -\frac{b^2}{a^2} \frac{1 \cdot (y-k) - (x-h) \frac{dy}{dx}}{(y-k)^2}
  5. Substitute the expression for dydx\frac{dy}{dx} into the equation for d2ydx2\frac{d^2y}{dx^2}.

    Substitute dydx=−b2(x−h)a2(y−k)\frac{dy}{dx} = -\frac{b^2(x-h)}{a^2(y-k)}:

    d2ydx2=−b2a2(y−k)−(x−h)(−b2(x−h)a2(y−k))(y−k)2\frac{d^2y}{dx^2} = -\frac{b^2}{a^2} \frac{(y-k) - (x-h) \left(-\frac{b^2(x-h)}{a^2(y-k)}\right)}{(y-k)^2} d2ydx2=−b2a2(y−k)+b2(x−h)2a2(y−k)(y−k)2\frac{d^2y}{dx^2} = -\frac{b^2}{a^2} \frac{(y-k) + \frac{b^2(x-h)^2}{a^2(y-k)}}{(y-k)^2}

    To simplify the numerator, find a common denominator:

    d2ydx2=−b2a2a2(y−k)2+b2(x−h)2a2(y−k)(y−k)2\frac{d^2y}{dx^2} = -\frac{b^2}{a^2} \frac{\frac{a^2(y-k)^2 + b^2(x-h)^2}{a^2(y-k)}}{(y-k)^2} d2ydx2=−b2a4a2(y−k)2+b2(x−h)2(y−k)3\frac{d^2y}{dx^2} = -\frac{b^2}{a^4} \frac{a^2(y-k)^2 + b^2(x-h)^2}{(y-k)^3}
  6. Use the original equation to simplify the numerator.

    From the original equation, (x−h)2a2+(y−k)2b2=1\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1.
    Multiply by a2b2a^2 b^2: b2(x−h)2+a2(y−k)2=a2b2b^2(x-h)^2 + a^2(y-k)^2 = a^2 b^2.
    Substitute this into the expression for d2ydx2\frac{d^2y}{dx^2}:

    d2ydx2=−b2a4a2b2(y−k)3\frac{d^2y}{dx^2} = -\frac{b^2}{a^4} \frac{a^2 b^2}{(y-k)^3} d2ydx2=−b4a2(y−k)3\frac{d^2y}{dx^2} = -\frac{b^4}{a^2(y-k)^3}
  7. Evaluate d2ydx2\frac{d^2y}{dx^2} at the point (1,1)(1,1).

    Substitute y=1y=1 into the expression for d2ydx2\frac{d^2y}{dx^2}:

    d2ydx2∣(1,1)=−b4a2(1−k)3\frac{d^2y}{dx^2} \Big|_{(1,1)} = -\frac{b^4}{a^2(1-k)^3}

    The second derivative at (1,1)(1,1) is −b4a2(1−k)3\boxed{-\frac{b^4}{a^2(1-k)^3}}.

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