# Focus and directrix of a parabola

3 videos
1 skill
A parabola is the set of all points equidistant from a point (called the focus) and a line (called the directrix). In this tutorial you will learn about the focus and the directrix, and how to find the equation of a parabola given its focus and directrix.

### Intro to focus & directrix

VIDEO 4:07 minutes
A parabola is the set of all points equidistant from a point (called the "focus") and a line (called the "directrix"). See this video to learn more about this.

### Equation of a parabola from focus & directrix

VIDEO 9:48 minutes
Sal derives the equation of a general parabola whose focus is (a,b) and directrix is y=k. He then uses this general formula in order to find the specific formula whose focus is (1,2) and directrix is y=-1.

### Equation of a parabola from focus & directrix

PRACTICE PROBLEMS
Given the focus and the directrix of a parabola, find its equation.

### Focus & directrix of a parabola from equation

VIDEO 11:29 minutes
Given the parabola equation y-23/4=-1/3(x-1)^2, Sal finds the parabola's focus and directrix using the general formula for a parabola whose focus is (a,b) and directrix is y=k.