RAJASTHAN ­ PET Rajasthan PET Solved Paper-2003

  • question_answer
    If\[x=a\text{ }cos\text{ }t,\text{ }y=b\text{ }sin\text{ }t,\]then\[\frac{dy}{dx}\]is equal to

    A)  \[-\frac{b}{a}\tan t\]

    B)  \[-\frac{b}{a}\cot t\]

    C)  \[-\frac{a}{b}\cot t\]

    D)  \[-\frac{a}{b}\tan t\]

    Correct Answer: B

    Solution :

     \[x=a\cos t,y=b\sin t\] \[\therefore \] \[\frac{dx}{dt}=-a\sin t,\] and \[\frac{dy}{dt}=b\cos t\] \[\therefore \] \[\frac{dy}{dx}=\frac{dy/dx}{dx/dt}\] \[=\frac{b\cos t}{-a\sin t}=-\frac{b}{a}\cot t\]


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