RAJASTHAN ­ PET Rajasthan PET Solved Paper-2003

  • question_answer
    If focal chord of a parabola\[{{y}^{2}}=4ax\]intercepted at b and k, then k is equal to

    A)  \[\frac{ab}{b-a}\]

    B)  \[\frac{b}{b-a}\]

    C)  \[\frac{a}{b-a}\]

    D)  \[\frac{ba}{a-b}\]

    Correct Answer: A

    Solution :

     Length of latusrectum of the parabola \[{{y}^{2}}=4ax\]is\[4a\]. \[\because \] Intercept points are b and k. \[\therefore \]latusrectum, \[4a=4.\frac{bk}{b+k}\] \[\Rightarrow \] \[a=\frac{bk}{b+k}\] \[\Rightarrow \] \[ab+ak=bk\] \[\Rightarrow \] \[k(b-a)=ab\] \[\Rightarrow \] \[k=\frac{ab}{b-a}\]


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