JEE Main & Advanced Mathematics Conic Sections Question Bank Parabola

  • question_answer
    The focus of the parabola \[4{{y}^{2}}-6x-4y=5\] is   [RPET 1997]

    A) (-8/5, 2)                                    

    B) (-5/8, 1/2)

    C) (1/2, 5/8)                                  

    D) (5/8, -1/2)

    Correct Answer: B

    Solution :

    Given equation of parabola written in standard form, we get                    \[4{{\left( y-\frac{1}{2} \right)}^{2}}=6(x+1)\Rightarrow {{\left( y-\frac{1}{2} \right)}^{2}}=\frac{3}{2}(x+1)\Rightarrow {{Y}^{2}}=\frac{3}{2}X\]                    where, \[Y=y-\frac{1}{2},\,\,X=x+1\]                    \[\therefore y=Y+\frac{1}{2},\,\,\,x=X-1\]                                         ?..(i)                 For focus \[X=a,\,\,Y=0\]                    \[\because 4a=\frac{3}{2}\Rightarrow a=\frac{3}{8}\Rightarrow x=\frac{3}{8}-1=-\frac{5}{8}\]                    \[y=0+\frac{1}{2}=\frac{1}{2}\], Focus\[=\left( -\frac{5}{8},\frac{1}{2} \right)\].


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