Chapter 10 - Analytic Geometry - 10.1 Parabolas - 10.1 Exercises - Page 967: 36

$${y^2} = - 2x$$

$$\eqalign{ & {\text{Focus }}\left( { - \frac{1}{2},0} \right) \cr & {\text{The focus of a parabola of the form }}{y^2} = 4px{\text{ is }}\left( {p,0} \right) \cr & {\text{Focus }}\left( { - \frac{1}{2},0} \right) \cr & {\text{Then }}p = - \frac{1}{2} \cr & {\text{And the equation is:}} \cr & {y^2} = 4px \cr & {y^2} = 4\left( { - \frac{1}{2}} \right)x \cr & {y^2} = - 2x \cr} $$