JCECE Engineering JCECE Engineering Solved Paper-2002

  • question_answer
    If\[x={{\sin }^{-1}}(3t-4{{t}^{3}})\]and\[y={{\cos }^{-1}}\sqrt{(1-{{t}^{2}})}\], then \[\frac{dy}{dx}\] is equal to:

    A) \[1/2\]                                 

    B)  \[2/5\]

    C)  \[3/2\]                                

    D)  \[1/3\]

    Correct Answer: D

    Solution :

    Given that                 \[x={{\sin }^{-1}}(3t-4{{t}^{3}})\] and        \[y={{\cos }^{-1}}\sqrt{1-{{t}^{2}}}\] Put         \[t=\sin \theta \], we get                 \[x={{\sin }^{-1}}(3\sin \theta -4{{\sin }^{3}}\theta )\] and        \[y={{\cos }^{-1}}\sqrt{1-{{\sin }^{2}}\theta }\] \[\Rightarrow \]               \[x={{\sin }^{-1}}(\sin 3\theta )\] and        \[y={{\cos }^{-1}}(\cos \theta )\] \[\Rightarrow \]               \[x=3\theta \]and\[y=\theta \] \[\Rightarrow \]               \[x=3{{\sin }^{-1}}t\]and\[y={{\sin }^{-1}}t\] On differentiating both sides \[\text{w}\text{.r}\text{.t}.t,\] respectively we get                 \[\frac{dx}{dt}=\frac{3}{\sqrt{1-{{t}^{2}}}}\]and\[\frac{dy}{dt}=\frac{1}{\sqrt{1-{{t}^{2}}}}\]


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