JCECE Engineering JCECE Engineering Solved Paper-2014

  • question_answer
    If\[y={{t}^{10}}+1\]and\[x={{t}^{8}}\], then \[\frac{{{d}^{2}}y}{d{{x}^{2}}}\] is equal to

    A) \[\frac{5}{2}t\]                                 

    B) \[20{{t}^{8}}\]

    C)  \[\frac{5}{16{{t}^{6}}}\]                                               

    D)   None of these

    Correct Answer: C

    Solution :

    Here,\[y={{t}^{10}}\]and\[x={{t}^{8}}+1\] \[\therefore \]  \[{{t}^{8}}=x-1\Rightarrow {{t}^{2}}={{(x-1)}^{1/4}}\] So,          \[y={{(x-1)}^{5/4}}+1\] On differentiating both sides w.r.t. x, we get                 \[\frac{dy}{dx}={{(x-1)}^{1/4}}\] Again, differentiating both sides w.r.t. x, we get \[\Rightarrow \]               \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=\frac{5}{16{{(x-1)}^{3/4}}}=\frac{5}{16{{({{t}^{2}})}^{3}}}=\frac{5}{16{{t}^{6}}}\]


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