Translations of Parabolas
On this web page you can explore the relationship between the
equation of a translated parabola and the coordinates of its vertex.
You've already learned that if you translate the
graph of y = x2 horizontally h units
and vertically k units then the equation of the translated
parabola is y = (x – h)2 + k.
You may also see this equation written as y = k + (x
– h)2 or y
– k = (x – h)2.
When you translate any equation horizontally, you can think of it as
replacing x in the equation with (x – h).
Likewise, a vertical translation replaces y with (y – k).
This sketch shows the graph of the parent function y = x2
in gray. The red parabola is its image after a translation. Drag the
vertex (h, k) to translate the image. Observe how the
coordinates of the vertex and the equation of the image change. Press
Start Over to move the vertex back to (0, 0). (Note: The
caret symbol, ^, represents an exponent, as on
- Drag the vertex to (2, 0). What is the equation of the red
- Drag the vertex so the equation is y = (x – 0)2
+ 4. What are the coordinates of the vertex now?
- Drag the red parabola to show a translation horizontally 2 units
4 units. What is the equation of the red parabola? What are the
coordinates of the vertex?
- In general, what are the coordinates of the vertex of the
parabola formed when the graph of y = x2 is
translated horizontally h units and vertically k units?
- How can this relationship help you find the equation of a
parabola if you are given only its graph?