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(3 points) Show that d/dx [tan⁻¹ x] = 1/(1+x2)

Mathematics

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Answer

ddx[tan⁡−1(x)]=11+x2\frac{d}{dx}[\tan^{-1}(x)] = \frac{1}{1+x^2}

Step-by-step solution

5 steps

To show that ddx[tan⁡−1(x)]=11+x2\frac{d}{dx}[\tan^{-1}(x)] = \frac{1}{1+x^2}, we can use implicit differentiation.

  1. Let y=tan⁡−1(x)y = \tan^{-1}(x).

    This means that x=tan⁡(y)x = \tan(y).

  2. Differentiate both sides of x=tan⁡(y)x = \tan(y) with respect to xx.

    We use the chain rule for the right side.

    ddx(x)=ddx(tan⁡(y))\frac{d}{dx}(x) = \frac{d}{dx}(\tan(y)) 1=sec⁡2(y)dydx1 = \sec^2(y) \frac{dy}{dx}
  3. Solve for dydx\frac{dy}{dx}.

    dydx=1sec⁡2(y)\frac{dy}{dx} = \frac{1}{\sec^2(y)}
  4. Use the trigonometric identity sec⁡2(y)=1+tan⁡2(y)\sec^2(y) = 1 + \tan^2(y).

    Substitute this into the expression for dydx\frac{dy}{dx}.

    dydx=11+tan⁡2(y)\frac{dy}{dx} = \frac{1}{1 + \tan^2(y)}
  5. Substitute xx back into the equation, since we know x=tan⁡(y)x = \tan(y).

    dydx=11+x2\frac{dy}{dx} = \frac{1}{1 + x^2}
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