RAJASTHAN ­ PET Rajasthan PET Solved Paper-2002

  • question_answer
    Intersection point of the tangents drawn to the parabola\[{{y}^{2}}=4ax\]from the points \[(at_{1}^{2},2a{{t}_{1}})\]and\[(at_{2}^{2},2a{{t}_{2}})\]is

    A)  \[(a{{t}_{1}}{{t}_{2}},a({{t}_{1}}+{{t}_{2}}))\]

    B)  \[(a({{t}_{1}}+{{t}_{2}}),a{{t}_{1}}{{t}_{2}})\]

    C)  \[(t_{1}^{2}t_{2}^{2},{{t}_{1}}+{{t}_{2}})\]

    D)  None of these

    Correct Answer: A

    Solution :

     Equation of tangent to the parabola\[{{y}^{2}}=4ax\] at the point\[(at_{1}^{2},2a{{t}_{1}})\]is \[2a{{t}_{1}}=2a(x+at_{1}^{2})\] \[\Rightarrow \] \[y{{t}_{1}}=x+at_{1}^{2}\]          ...(i) Similarly, equation of tangent at the point\[(at_{2}^{2},2a{{t}_{2}})\]is \[2ya{{t}_{2}}=2a(x+at_{2}^{2})\] \[\Rightarrow \] \[y{{t}_{2}}=x+at_{2}^{2}\]              ...(ii) On solving Eqs. (i) and (ii), we get \[y=a({{t}_{1}}+{{t}_{2}}),x=a{{t}_{1}}{{t}_{2}}\] \[\therefore \]Intersection point\[[a{{t}_{1}}{{t}_{2}},a({{t}_{1}}+{{t}_{2}})]\]


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