JEE Main & Advanced Mathematics Conic Sections Question Bank Parabola

  • question_answer
    The two parabolas \[{{y}^{2}}=4x\] and \[{{x}^{2}}=4y\] intersect at a point P, whose abscissa is not zero, such that

    A)            They both touch each other at P

    B)            They cut at right angles at P

    C)            The tangents to each curve at P make complementary angles with the x-axis

    D)            None of these

    Correct Answer: C

    Solution :

               Solving \[{{x}^{2}}=4y\]and \[{{y}^{2}}=4x,\]we get \[x=0,\,\,y=0\] and \[x=4,\,y=4\]. Therefore the co-ordinates of P are (4,4). The equations of the tangents to the two parabolas at (4,4) are \[2x-y-4=0\]                   .....(i)                    \[x-2y+4=0\]                                   .....(ii)                    Now, \[{{m}_{1}}=\]Slope of (i) \[=2,\]\[{{m}_{2}}=\]Slope of (ii) \[=\frac{1}{2}\]                    \\[{{m}_{1}}{{m}_{2}}=1\,\,\,i.e.,\,\,\,\tan {{\theta }_{1}}\tan {{\theta }_{2}}=1\].


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