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In the adjacent figure a parabola is drawn to pass through the vertices \mathrm{B}, \mathrm{C}\: \text{and} \: \mathrm{D} of the square \mathrm{ABCD}. If \mathrm{\mathrm{A}(2,1), \mathrm{C}(2,3)} then focus of this parabola is -



 

Option: 1

\left(1, \frac{11}{4}\right)


 


Option: 2

\left(2, \frac{11}{4}\right)
 


Option: 3

\left(3, \frac{13}{4}\right)
 


Option: 4

\left(2, \frac{13}{4}\right)


Answers (1)

best_answer

Clearly \mathrm{AC} is parallel to y-axis. It's midpoint is (2,2). Thus \mathrm{B} \equiv(1,2).

Parabola will be in the form of \mathrm{(\mathrm{x}-2)^2=\lambda(\mathrm{y}-3).}

It passes through (3,2)

\mathrm{\Rightarrow 1=-\lambda}. Thus parabola is \mathrm{(\mathrm{x}-2)^2=-1(\mathrm{y}-3).}

It focus is \mathrm{x-2=0 . y-3=-\frac{1}{4}}, i.e., \mathrm{\left(2, \frac{11}{4}\right).}

Hence option 2 is correct.

Posted by

manish

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