JEE Main & Advanced Mathematics Differential Equations Question Bank Variable Separable type differential equations

  • question_answer
    The solution of \[(x\sqrt{1+{{y}^{2}}})dx+(y\sqrt{1+{{x}^{2}}})dy=0\] is

    A)                 \[\sqrt{1+{{x}^{2}}}+\sqrt{1+{{y}^{2}}}=c\]       

    B)                 \[\sqrt{1+{{x}^{2}}}-\sqrt{1+{{y}^{2}}}=c\]

    C)                 \[{{(1+{{x}^{2}})}^{3/2}}+{{(1+{{y}^{2}})}^{3/2}}=c\]             

    D)                 None of these

    Correct Answer: A

    Solution :

                       Given equation is, \[(x\sqrt{1+{{y}^{2}}})dx+(y\sqrt{1+{{x}^{2}}})dy=0\]                    Þ \[x\sqrt{1+{{y}^{2}}}dx=-y\sqrt{1+{{x}^{2}}}dy\]         Þ \[\int_{{}}^{{}}{\frac{x}{\sqrt{1+{{x}^{2}}}}dx+}\int_{{}}^{{}}{\frac{y}{\sqrt{1+{{y}^{2}}}}dy=c}\]                 Þ \[\sqrt{1+{{x}^{2}}}+\sqrt{1+{{y}^{2}}}=c\].


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