Q92 / 180 · COMEDK 2018 · Mathematics
The ends of the latusrectum of the parabola $x^{2}+10 x-16 y+25=0$ are
- Correct answerA$(3,4),(-13,4)$
- 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'.