Chapter 10 - Analytic Geometry - 10.1 Parabolas - 10.1 Exercises - Page 967: 37

$${x^2} = y$$

$$\eqalign{ & {\text{directrix }}y = - \frac{1}{4} \cr & {\text{The directrix of a parabola of the form }}{x^2} = 4py{\text{ is }}y = - p \cr & \underbrace {y = - \frac{1}{4}}_{y = - p},\,\,p = \frac{1}{4} \cr & {\text{Then, the equation is:}} \cr & {x^2} = 4\left( {\frac{1}{4}} \right)y \cr & {x^2} = y \cr} $$