Directrix

Definition

The directrix is a key concept in the study of conic sections, which are the shapes formed by the intersection of a plane and a cone. It is a fixed line that, along with the focus, defines the shape and properties of an ellipse, hyperbola, or parabola.

5 Must Know Facts For Your Next Test

1. The directrix is a fixed, imaginary line that, along with the focus, defines the shape and properties of a conic section.
2. The distance from any point on the conic section to the focus is in a constant ratio to the distance from that point to the directrix.
3. The eccentricity of a conic section is determined by the ratio of the distance from the center to the focus and the distance from the center to the directrix.
4. The latus rectum is the chord of the conic section that is parallel to the directrix.
5. The directrix is an important concept in the study of conic sections, as it helps to understand the geometry and equations of these shapes.

Review Questions

• Explain how the directrix and focus together define the shape and properties of a conic section.
  • The directrix and focus work together to define the shape and properties of a conic section. The distance from any point on the conic section to the focus is in a constant ratio to the distance from that point to the directrix. This ratio, known as the eccentricity, determines the type of conic section (ellipse, hyperbola, or parabola) and its specific characteristics, such as the lengths of the major and minor axes, the location of the center, and the shape of the curve.
• Describe the relationship between the directrix, focus, and latus rectum of a conic section.
  • The latus rectum is the chord of the conic section that is parallel to the directrix. The distance from the focus to the latus rectum is equal to the distance from the center to the directrix. This relationship is important because it allows for the calculation of the equation of the conic section and the determination of its properties, such as the eccentricity and the lengths of the major and minor axes.
• Analyze how the concept of the directrix is applied in the study of conic sections in polar coordinates.
  • In the study of conic sections in polar coordinates, the directrix plays a crucial role in defining the shape and properties of the curves. The polar equation of a conic section is often expressed in terms of the distance from the focus to the directrix, the eccentricity, and the angle between the polar axis and the line perpendicular to the directrix. This representation allows for a deeper understanding of the geometric properties of conic sections and their applications in various fields, such as astronomy, engineering, and optics.

Related terms

Focus: The focus is a point that, along with the directrix, defines the shape and properties of a conic section. The distance from any point on the conic section to the focus is in a constant ratio to the distance from that point to the directrix.

Eccentricity: Eccentricity is a measure of how elongated or flattened a conic section is, and it is determined by the ratio of the distance from the center to the focus and the distance from the center to the directrix.

Latus Rectum: The latus rectum is the line segment that passes through the focus and is perpendicular to the major axis of an ellipse or hyperbola. It is the chord of the conic section that is parallel to the directrix.