JEE Main & Advanced Mathematics Conic Sections Question Bank Parabola

  • question_answer
    The equation of the latus rectum of the parabola represented by equation \[{{y}^{2}}+2Ax+2By+C=0\] is

    A)            \[x=\frac{{{B}^{2}}+{{A}^{2}}-C}{2A}\]                                        

    B)            \[x=\frac{{{B}^{2}}-{{A}^{2}}+C}{2A}\]

    C)            \[x=\frac{{{B}^{2}}-{{A}^{2}}-C}{2A}\]                                         

    D)            \[x=\frac{{{A}^{2}}-{{B}^{2}}-C}{2A}\]

    Correct Answer: B

    Solution :

               \[{{(y+B)}^{2}}=-2Ax-C+{{B}^{2}}=-2A\left( x+\frac{C}{2A}-\frac{{{B}^{2}}}{2A} \right)\]            Equation of latus rectum \[x+\lambda =0\]            Vertex \[=\left( \frac{-C+{{B}^{2}}}{2A},B \right)\], focus \[\equiv \left( \frac{-C+{{B}^{2}}}{2A}-\frac{A}{2},B \right)\]                    Equation of L.R. is \[x=\frac{-C+{{B}^{2}}}{2A}-\frac{A}{2}=\frac{{{B}^{2}}-{{A}^{2}}-C}{2A}\].


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