JEE Main & Advanced Mathematics Differentiation Question Bank Partial Differentiation

  • question_answer
    If \[z={{\tan }^{-1}}\left( \frac{x}{y} \right)\], then \[{{z}_{x}}:{{z}_{y}}=\]

    A)            \[y:x\]

    B)            \[x:y\]

    C)            \[-y:x\]

    D)            \[-x:y\]

    Correct Answer: C

    Solution :

                       \[\frac{\partial z}{\partial x}=\frac{1}{1+\frac{{{x}^{2}}}{{{y}^{2}}}}.\frac{1}{y}=\frac{y}{{{x}^{2}}+{{y}^{2}}}\]                    \[\frac{\partial z}{\partial y}=\frac{1}{1+\frac{{{x}^{2}}}{{{y}^{2}}}}.\left( -\frac{x}{{{y}^{2}}} \right)=-\frac{x}{{{x}^{2}}+{{y}^{2}}}\]                    \[\therefore \] \[\frac{\partial z}{\partial x}:\frac{\partial z}{\partial y}=y:-x\] i.e.,  \[{{z}_{x}}:{{z}_{y}}=-y:x\]


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