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RAJASTHAN ­ PET Rajasthan PET Solved Paper-2004

  • question_answer
    If ordinate of a point on the parabola\[{{y}^{2}}=64x\]is 8, then the equation of tangent at this point is

    A)  \[4x-y+4=0\]     

    B)  \[4x+y+4=0\]

    C)  \[x+4y-4=0\]     

    D)  None of these

    Correct Answer: A

    Solution :

     The ordinate of a point on the parabola \[{{y}^{2}}=64x\] is\[y=8,\] then     \[{{(8)}^{2}}=64x\Rightarrow x=1\] Hence, equation of tangent line at point (1, 8) is \[y{{y}_{1}}=2a(x+{{x}_{1}})\] \[\Rightarrow \] \[y(8)=2.16(x+1)\] \[\Rightarrow \] \[y=4(x+1)\] \[\Rightarrow \] \[4x-y+4=0\]


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