## Calculus 8th Edition

The equation of a parabola becomes: $y^{2}=-x$ which has focus $(-\frac{1}{4},0)$ and directrix is $x=\frac{1}{4}$.
The equation of a parabola with vertex $(0,0)$ is $y^{2}=4px$.It has focus $(p,0)$ and directrix $x=-p$. Take $(-1,1)$ a point shown on the curve. Thus, $(1)^{2}=4p(-1)$ or, $p=-\frac{1}{4}$ Hence, the equation of a parabola becomes: $y^{2}=-x$ which has focus $(-\frac{1}{4},0)$ and directrix is $x=\frac{1}{4}$.