In Exercises 1–4, find the focus and directrix of each parabola with the given equation. Then match each equation to one of the graphs that are shown and labeled (a)–(d). x^2 = - 4y

Key Concepts

Parabola Definition

A parabola is a symmetric curve formed by the intersection of a cone with a plane parallel to its side. In algebra, parabolas can be represented by quadratic equations, typically in the form y = ax^2 + bx + c or x = ay^2 + by + c. The orientation of the parabola (opening upwards, downwards, left, or right) depends on the coefficients in the equation.

Focus and Directrix

The focus of a parabola is a fixed point located inside the curve, while the directrix is a line outside the curve. The defining property of a parabola is that any point on the curve is equidistant from the focus and the directrix. For the equation x^2 = -4y, the focus and directrix can be derived from the standard form of a parabola.

Standard Form of a Parabola

The standard form of a parabola that opens vertically is given by the equation (x - h)^2 = 4p(y - k), where (h, k) is the vertex, and p is the distance from the vertex to the focus (and also to the directrix). For the equation x^2 = -4y, it can be rewritten to identify the vertex and the value of p, which helps in determining the focus and directrix.