Chapter 11: Parametric Equations and Polar Coordinates - Section 11.6 - Conic Sections - Exercises 11.6 - Page 678: 12

Focus: $(-\displaystyle \frac{1}{2},0)\quad$ Directrix: $x=\displaystyle \frac{1}{2}$ .

$y^{2}=-4px \quad \Rightarrow \quad $the parabola opens left, $y^{2}=-2x$ $y^{2}=-2(\displaystyle \frac{4}{4})x$ $y^{2}=-4(\displaystyle \frac{1}{2})x \quad \Rightarrow \quad p=\frac{1}{2}$ Focus: $(-\displaystyle \frac{1}{2},0)\quad$ Directrix: $x=\displaystyle \frac{1}{2}$