Q92 / 180 · COMEDK 2018 · Mathematics

The ends of the latusrectum of the parabola $x^{2}+10 x-16 y+25=0$ are

  • Correct answer
    A
    $(3,4),(-13,4)$
  • B
    $(5,-8),(-5,8)$
  • C
    $(3,-4),(13,4)$
  • D
    $(-3,4),(13,-4)$

Solution

Given, equation of parabola is $$ x^{2}+10 x-16 y+25=0 $$ It can be rewritten as $$ (x+5)^{2}=16 y $$ Here $a=4$ and vertex $\equiv(-5,0)$ and focus $=(-5,4)$ So, $y$-coordinate of ends of latusrectum will be 4 . Putting in equation, we have $(x+5)^{2}=16 \times 4=64$ $\Rightarrow \quad x+5=\pm 8$ So, $\quad x=3,-13$ Substituting $x$ in Eq. (i), we get $y=4,4$ Hence, ends of latusrectum will be $(3,4)$ and $(-13,4)$.

Hence, the correct answer is option: 'A'.

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