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# What is the directrix of an ellipse?

In geometry, an ellipse is a closed curve where the sum of the distances from any two points on the curve (the major and minor axes) to a single point (the focus) are equal. The directrix of an ellipse is a line used to define its shape. In this blog post, we will explore what the directrix of an ellipse is and how it is used to define the shape of this geometric figure.

The directrix of an ellipse is a line that is perpendicular to the major axis at a distance of 2a from the center, where a is the semi-major axis. The directrix can be used to define the shape of an ellipse because it determines the eccentricity, which is a measure of how "flat" or "stretched out" an ellipse is. Eccentricity is calculated using the formula e = c/a, where c is the distance from the center to the focus and a is the semi-major axis.

An ellipse with a small eccentricity (closer to 0) will be more circular in shape, while an ellipse with a large eccentricity (closer to 1) will be more "stretched out." The directrix can also be used to find the focii of an ellipse. Recall that there are two focii for an ellipse, located on either side of the center at a distance of c from it. To find them, draw lines perpendicular to the directrix at both ends of the major axis. The intersection of these lines with the directrix will be one of the focii, and the other focii will be located symmetrically on either side of it.

In conclusion, we have explored what the directrix of an ellipse is and how it can be used to define this geometric figure. We have also seen how it can be used to calculate important properties such as eccentricity and finding the focii. We hope that this article has helped you understand this concept better!

## FAQ

### How do you find the Directrix of an ellipse?

There are a few different ways to find the Directrix of an ellipse, but one of the most common is by using the Focus Points. The Directrix is a line that is perpendicular to the major and minor axes at the focus points. Another way to find the Directrix is by using the equation of the ellipse. The Directrix is always at a constant distance from the focus points, so if you can find the focus points, you can find the Directrix.

### How do you find the Directrix?

There are a few different ways to find the Directrix of an ellipse, but one of the most common is by using the Focus Points. The Directrix is a line that is perpendicular to the major and minor axes at the focus points. Another way to find the Directrix is by using the equation of the ellipse. The Directrix is always at a constant distance from the focus points, so if you can find the focus points, you can find the Directrix.

### What is a Directrix?

A Directrix is a line that is perpendicular to the major and minor axes at the focus points. Another way to find the Directrix is by using the equation of the ellipse. The Directrix is always at a constant distance from the focus points, so if you can find the focus points, you can find the Directrix.

### What is Directrix and eccentricity?

The Directrix is a line that is perpendicular to the major and minor axes at the focus points. The eccentricity is the ratio of the distance between the focus points and the Directrix to the length of the major axis. The eccentricity is always between 0 and 1, with 0 being a circle and 1 being a line.