JEE Main & Advanced JEE Main Paper (Held On 22 April 2013)

  • question_answer
    Consider the differential equation \[\frac{dy}{dx}=\frac{{{y}^{3}}}{2(x{{y}^{2}}-{{x}^{2}})}:\] Statement 1: The substitution \[z={{y}^{2}}\] transforms the above equation into a first order homogenous differential equation. Statement 2: The solution of this differential equation is \[{{y}^{2}}e\frac{-{{y}^{2}}}{x}=C.\]

    A)  Both statements are false.

    B)  Statement 1 is rue and statement 2 is false.

    C)  Statement 1 is false. Statement 2 is true

    D)  Both statement s are true.

    Correct Answer: D

    Solution :

     Give differential equation is \[\frac{dy}{dx}=\frac{{{y}^{3}}}{2(xy-{{x}^{2}})}\] But substituting \[z={{y}^{2}},\]we get diff. eqn. as \[\frac{dz}{dx}=\frac{2{{z}^{2}}}{2(xz-{{x}^{2}})}=\frac{{{z}^{2}}}{xz-{{x}^{2}}}\] Now, \[\frac{dz}{dx}=\frac{2{{z}^{2}}}{2(xz-{{x}^{2}})}=\frac{{{z}^{2}}}{xz-{{x}^{2}}}\] Hence, statement -1 is true. Now, \[{{y}^{2}}{{e}^{-{{y}^{2}}/x}}=C\]satisfies the given diff. equation \[\therefore \] it is the solution of given diff. equation. Thus, statement -2 is also true.


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