Conics Instructional Unit
Day 2 - Introduction to Parabolas
by
Mandy Stein
Parabola
The locus of all points P(x,y) equidistant from a fixed point, called the focus, and a fixed line, called the directrix.
To construct a parabola in Geometer’s Sketchpad
1. Choose the focus, a point, and the directrix, a line
2. Construct a line segment between the focus and a point, called A, on the directrix
3. Construct the perpendicular bisector of the line segment
4. Construct a line perpendicular to the directrix through point A
5. Tracing the intersection of this line and the perpendicular bisector will give the locus of all points equidistant from the focus and the directrix
Click here for the GSP file with a vertical directrix
Click here to the GSP file with a horizontal directrix