JEE Main & Advanced Mathematics Differentiation Question Bank Partial Differentiation

  • question_answer
    If \[z={{\sin }^{-1}}\left( \frac{x+y}{\sqrt{x}+\sqrt{y}} \right)\], then \[x\frac{\partial z}{\partial x}+y\frac{\partial z}{\partial y}\] is equal to [EAMCET 1998; Orissa JEE 2000]

    A)            \[\frac{1}{2}\sin z\]

    B)            \[\frac{1}{2}\tan z\]

    C)            \[0\]

    D)            None of these

    Correct Answer: B

    Solution :

                       \[\sin z\] is homogeneous in x, y of degree 1/2.                    \[\therefore \] \[x\frac{\partial }{\partial x}(\sin z)+y\frac{\partial }{\partial y}(\sin z)=\frac{1}{2}\sin z\]                    Þ\[\frac{dv}{dt}\]                    Þ \[x\frac{\partial z}{\partial x}+y\frac{\partial z}{\partial y}=\frac{1}{2}\tan z\].


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