12th Class Mathematics Sample Paper Mathematics Olympiad - Sample Paper-5

  • question_answer
    The solution of \[{{\mathbf{x}}^{\mathbf{2}}}+{{\mathbf{y}}^{\mathbf{2}}}\frac{dy}{dx}=\mathbf{4}\], is:

    A)  \[{{x}^{3}}-{{y}^{3}}=12x+c'\]      

    B)  \[{{x}^{3}}+{{y}^{3}}=12x+c'\]

    C)  \[{{y}^{3}}+{{x}^{3}}=12x+c'\]    

    D)  None of these

    Correct Answer: B

    Solution :

    [b] \[\because {{x}^{2}}+{{y}^{2}}\frac{dy}{dx}=4\] \[\Rightarrow {{y}^{2}}\frac{dy}{dx}=\left( 4-{{x}^{2}} \right)\] Integrating, we have \[\int{{{y}^{2}}.dy}=\int{(4-{{x}^{2}})}.dy\] \[\Rightarrow \frac{{{y}^{3}}}{3}=4x-\frac{{{x}^{3}}}{3}+c\] \[\Rightarrow {{y}^{3}}+{{x}^{3}}=12x+c'\] Hence, option [b] is the required solution.


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