BCECE Engineering BCECE Engineering Solved Paper-2003

  • question_answer
    The differential equation of the family of curves \[y=a\cos (x+b)\]is :

    A) \[\frac{{{d}^{2}}y}{d{{x}^{2}}}-y=0\]                      

    B)                   \[\frac{{{d}^{2}}y}{d{{x}^{2}}}+y=0\]

    C)                   \[\frac{{{d}^{2}}y}{d{{x}^{2}}}+2y=0\]  

    D)                   none of these

    Correct Answer: B

    Solution :

    Key Idea: If there are \[n\] arbitrary constant, then we can differentiate maximum \[n\] times. We have, \[y=a\cos (x+b)\]                        ...(i) On differentiating w.r.t. \[x,\]we get \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=-a\cos (x+b)\] \[=-y\]                  [from(i)]                 \[\Rightarrow \]                               \[\frac{{{d}^{2}}y}{d{{x}^{2}}}+y=0\]


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