RAJASTHAN ­ PET Rajasthan PET Solved Paper-2005

  • question_answer
    The curve represented by the parametric equations \[x=3(\cos t+\sin t),y=4\]\[(cos\text{ }t-sin\text{ }t)\]is

    A)  a parabola        

    B)  an ellipse

    C)  a hyperbola      

    D)  None of these

    Correct Answer: B

    Solution :

     Given, \[x=3(cos\text{ }t+sin\text{ }t)\] \[\Rightarrow \] \[\frac{x}{3}=\cos t+\sin t\]     ...(i) and          \[y=4(cos\text{ }t-sin\text{ }t)\] \[\Rightarrow \] \[\frac{y}{4}=\cos t-\sin t\]    ...(ii) On squaring and adding Eqs. (i) and (ii), \[{{\left( \frac{x}{3} \right)}^{2}}+{{\left( \frac{y}{4} \right)}^{2}}={{(\cos t+\sin t)}^{2}}+{{(\cos t-\sin t)}^{2}}\] \[\Rightarrow \]\[\frac{{{x}^{2}}}{9}+\frac{{{y}^{2}}}{16}=1+2\cos t\sin t+1-2\cos t\sin t\] \[\Rightarrow \] \[\frac{{{x}^{2}}}{9}+\frac{{{y}^{2}}}{16}=2\] \[\Rightarrow \] \[\frac{{{x}^{2}}}{18}+\frac{{{y}^{2}}}{32}=1\] Which represents an ellipse.


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