key term - Major axis

Definition

The major axis is the longest diameter of an ellipse, passing through its foci and defining the shape of the ellipse. It is crucial for understanding the geometry of ellipses, as it provides important information about the orientation and dimensions of the ellipse. The length of the major axis is directly related to the ellipse's eccentricity and overall size, influencing how it appears on a coordinate plane.

5 Must Know Facts For Your Next Test

1. The length of the major axis is twice the length of the semi-major axis, which extends from the center to one end of the ellipse.
2. In standard form, an ellipse centered at the origin with a horizontal major axis is represented as $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$, where $a$ is half the length of the major axis and $b$ is half the length of the minor axis.
3. The major axis can be horizontal or vertical depending on how the ellipse is oriented in relation to the coordinate axes.
4. The distance between the foci is determined by the formula $$c = \sqrt{a^2 - b^2}$$, where $c$ is half the distance between foci, $a$ is half the major axis, and $b$ is half the minor axis.
5. In real-world applications, such as planetary orbits, celestial bodies often follow elliptical paths where their major axes define their orbital characteristics.

Review Questions

• How does understanding the major axis help in sketching an ellipse accurately?
  • Knowing where the major axis is located allows you to establish key dimensions and orientation when sketching an ellipse. The endpoints of the major axis help you define its width, while knowing it passes through the foci aids in ensuring that points on either side remain equidistant from these focal points. This foundational information leads to a more accurate representation of an ellipse's shape.
• What role does eccentricity play in determining the characteristics of an ellipse related to its major axis?
  • Eccentricity quantifies how elongated an ellipse is compared to a circle, influencing its overall shape. The major axis length directly affects eccentricity; as it increases relative to its minor axis, eccentricity increases, making the ellipse appear flatter. Understanding this relationship allows for deeper insight into how changes in one dimension impact other geometric properties.
• Evaluate how changes in the lengths of both axes affect an ellipse's visual appearance and mathematical properties.
  • When both axes change length simultaneously, they transform how an ellipse looks and behaves mathematically. If only the major axis increases while keeping the minor axis constant, it results in a flatter appearance and higher eccentricity. Conversely, if both axes increase proportionately, maintaining their ratio will preserve its circular shape. This interplay showcases how different dimensions can influence not only aesthetics but also mathematical relationships such as area and perimeter.

Related terms

minor axis:

The minor axis is the shortest diameter of an ellipse, perpendicular to the major axis, and also passes through the center of the ellipse.

foci:

Foci are two fixed points located along the major axis of an ellipse; the sum of the distances from any point on the ellipse to these two points is constant.

eccentricity: Eccentricity is a measure of how much an ellipse deviates from being circular, calculated as the ratio of the distance between the foci and the length of the major axis.