JEE Main & Advanced Mathematics Conic Sections Question Bank Parabola

  • question_answer
    The locus of the middle points of the chords of the parabola \[{{y}^{2}}=4ax\]which passes through the origin [RPET 1997; UPSEAT 1999]

    A)            \[{{y}^{2}}=ax\]                         

    B)            \[{{y}^{2}}=2ax\]

    C)            \[{{y}^{2}}=4ax\]                       

    D)            \[{{x}^{2}}=4ay\]

    Correct Answer: B

    Solution :

               Any line through origin (0,0) is \[y=mx\]. It intersects \[{{y}^{2}}=4ax\] in \[\left( \frac{4a}{{{m}^{2}}},\frac{4a}{m} \right)\].            Mid point of the chord is \[\left( \frac{2a}{{{m}^{2}}},\frac{2a}{m} \right)\]                    \[x=\frac{2a}{{{m}^{2}}},\]\[y=\frac{2a}{m}\]Þ \[\frac{2a}{x}=\frac{4{{a}^{2}}}{{{y}^{2}}}\] or \[{{y}^{2}}=2ax\],            which is a parabola.


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