MCQ
A point on the parabola whose focus is $S(1,-1)$ and whose vertex is $A(1,1)$ is
  • $\left(3, \frac{1}{2}\right)$
  • B
    (1, 2)
  • C
    $\left(2, \frac{1}{2}\right)$
  • D
    (2, 2)

Answer

Correct option: A.
$\left(3, \frac{1}{2}\right)$
(A)
Equation of parabola having vertex ( $p, q$ ) and
focus $(p, b+q)$ is given by
$(x-p)^2=4 b(y-q)$
Given, vertex $A=(1,1)$ and focus $S=(1,-1)$
$\therefore p=1, q=1, b=-2$
∴ Equation of parabola is
$(x-1)^2=4(-2)(y-1)$
i.e. $x^2-2 x+8 y-7=0$
Only $\left(3, \frac{1}{2}\right)$ satisfies the above equation of parabola.

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