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The abscissa and ordinate of the end points  \mathrm { A }  and   \mathrm { B }  of a focal chord of the parabola   \mathrm { y^2=4 x }  are respectively the roots of  \mathrm { x^2-3 x+a=0 }  and  \mathrm { y^2+6 y+b=0 }  . The equation of the circle with \mathrm { AB } as diameter is
 

Option: 1

\mathrm { x^2+y^2-3 x+6 y+3=0}


Option: 2

\mathrm { x^2+y^2-3 x+6 y-3=0}


Option: 3

\mathrm { x^2+y^2-3 x+6 y-2=0}


Option: 4

\mathrm { x^2+y^2-3 x-6 y-3=0}


Answers (1)

best_answer

\mathrm {t_1 t_2=-1}  as  \mathrm {A B}   is focal chord.

\begin{gathered} \mathrm { x^2-3 x+a=0 ; x_1+x_2=3 \text { and } x_1 x_2=a }\\ \mathrm {y^2+6 y+b=0 ; y_1+y_2=-6 \text { and } y_1 y_2=b} \\ \mathrm {x_1 x_2=\frac{1}{t_1^2} t_1^2=1=a} \end{gathered}
\begin{aligned} & \mathrm {y_1 y_2=2 t_1\left(-\frac{2}{t_1}\right)=-4=b }\\ & \mathrm {a=1, b=-4} \end{aligned}
Equation of circle \mathrm{AB}  is diameter
\mathrm{ x^2+y^2-3 x+6 y-3=0 \text {. } }

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Deependra Verma

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