x^y . y^x = 1: find dy/dx

1. A.
   $-\dfrac{(y + x\log y)}{(x + y\log x)} \cdot \dfrac{y}{x}$
2. B.
   $\dfrac{(y + x\log y)}{(x + y\log x)} \cdot \dfrac{y}{x}$
3. C.
   $-\dfrac{(x + y\log y)}{(y + x\log x)} \cdot \dfrac{y}{x}$
4. D.
   $\dfrac{y}{x}$

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1. A.
   $\dfrac{y^2(1 + \log y)}{x^2(1 - \log x)}$
2. B.
   $\dfrac{y^2(1 + \log x)}{x^2(1 - \log y)}$
3. C.
   $\dfrac{-y^2(1 - \log x)}{x^2(1 - \log y)}$
4. D.
   $\dfrac{-x^2(1 - \log x)}{y^2(1 - \log y)}$

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