Theory
An ellipse consists of all points that have the same total distance to two given points, called focal points, or foci.
The following distances are important to describe an ellipse:
Semi-major axis ():
The greatest distance from the center of the ellipse to any point on the ellipse.
Semi-minor axis ():
The shortest distance from the center of the ellipse to any point on the ellipse.
Rule
A circle is a special case of an ellipse, where the focal points coincide and the semi-major and semi-minor axes are equal.
Example 1
Find the standard equation of an ellipse with a semi-major axis of and a semi-minor axis of
Example 2
Show that is the equation of an ellipse
To show that this equation represents an ellipse, you need to change it into the form of the standard equation of an ellipse. You can do that like this:
Because you’ve been able to change the expression into the form of the standard equation of an ellipse, you’ve shown that is an ellipse with semi-minor axis and semi-major axis .