CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2000

  • question_answer
    If \[x=\frac{1-{{t}^{2}}}{1+{{t}^{2}}}\]and \[y=\frac{2t}{1+{{t}^{2}}}\]then \[\frac{dy}{dx}\]

    A)  \[-y/x\]                              

    B)  \[y/x\]

    C)  \[-x/y\]                              

    D)  \[x/y\]

    Correct Answer: C

    Solution :

     Equation \[x=\frac{1-{{t}^{2}}}{1+{{t}^{2}}}\]and \[y=\frac{2t}{1+{{t}^{2}}}\] Put \[t=\tan \theta \Rightarrow x=\frac{1-{{\tan }^{2}}\theta }{1+{{\tan }^{2}}\theta }\] \[\Rightarrow \]\[x=\cos 2\theta \] \[\Rightarrow \]\[y=\frac{2\tan \theta }{1+{{\tan }^{2}}\theta }\Rightarrow y=\sin 2\theta ,x=\cos 2\theta \] \[\frac{dx}{d\theta }=-2\sin 2\theta ,\frac{dy}{d\theta }=2\cos 2\theta \] \[\frac{dy}{dx}=-\frac{2\cos 2\theta }{2\sin 2\theta }=-x/y\]


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