BCECE Engineering BCECE Engineering Solved Paper-2002

  • question_answer
    If \[y=\cos \,t\] and\[x=\sin t,\], then \[\frac{{{d}^{2}}y}{d{{x}^{2}}}\]is equal to:

    A) \[\frac{y}{x}\]                   

    B)         \[\frac{x}{y}\]                  

    C)                  0                            

    D)         none of these

    Correct Answer: D

    Solution :

    Given that,\[y=\cos t,x=\sin t\] On differentiating both sides w.r.t. t, we get \[\frac{dy}{dx}=-\sin \,t,\frac{dx}{dt}=\cos t\]                 \[\therefore \]  \[\frac{dy}{dx}=\frac{dy}{dt}\times \frac{dt}{dx}\]                                 \[=\frac{-\sin t}{\cos t}=-\tan t\] Again differentiating, we get \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=-{{\sec }^{2}}t.\frac{dt}{dx}\]                 \[=-{{\sec }^{2}}t.\frac{1}{\cos t}\]                 \[=-\frac{1}{{{\cos }^{3}}t}\]                 \[=-\frac{1}{{{y}^{3}}}\]


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