Question

The equation of directrix of conic $x^2+2x-y^2+5=0$ is

• A. $x=\pm 1$
• B. $y=\pm 2$
• C. $y=\pm \sqrt{2}$
• D. $x=-1\pm \sqrt{2}$

Answer 1

Answer: (C)

$(x+1{)}^2-y^2=-4\Rightarrow \frac{y^2}{4}-\frac{(x+1{)}^2}{4}=1$
$\therefore e=\sqrt{2}$ and directrix is $y=\pm \frac{b}{e}$.