Ellipse Focus and Directrix Calculator

Solve ellipse properties from axes, focus distance, or eccentricity. View formulas clearly. Export clean records for lessons, homework, and exam preparation.

Ellipse Calculator Form

Example Data Table

Case Center Orientation a b c e Directrices
Example 1 (0, 0) Horizontal 5 3 4 0.8 x = -6.25 and x = 6.25
Example 2 (2, -1) Vertical 7 4 5.744563 0.820652 y = -9.53125 and y = 7.53125
Example 3 (-3, 2) Horizontal 9 6 6.708204 0.745356 x = -15.074767 and x = 9.074767

Formula Used

1. For an ellipse, c² = a² - b².

2. Eccentricity is e = c / a.

3. Horizontal form: ((x - h)² / a²) + ((y - k)² / b²) = 1.

4. Vertical form: ((x - h)² / b²) + ((y - k)² / a²) = 1.

5. Horizontal foci are (h ± c, k).

6. Vertical foci are (h, k ± c).

7. Horizontal directrices are x = h ± a/e.

8. Vertical directrices are y = k ± a/e.

9. Major axis length = 2a and minor axis length = 2b.

10. Latus rectum length = 2b² / a.

How to Use This Calculator

  1. Select the input method that matches your known values.
  2. Choose whether the major axis is horizontal or vertical.
  3. Enter the center coordinates h and k.
  4. Fill the relevant fields for the chosen method.
  5. Click the calculate button to generate the ellipse details.
  6. Review focus points, directrices, vertices, and equation.
  7. Download the result as a CSV file or PDF file.

About Ellipse Focus and Directrix Calculations

Understand Key Ellipse Parts

An ellipse has a center, two foci, two directrices, and two axes. These parts describe its shape and position. The semi-major axis controls the longer direction. The semi-minor axis controls the shorter direction. Together, they define the curve clearly.

Why Focus and Directrix Matter

The focus and directrix explain the geometric definition of an ellipse. Any point on the curve keeps a constant ratio between its distance from a focus and its distance from a matching directrix. That ratio is the eccentricity. It is always less than one for an ellipse.

Useful Input Options

This calculator accepts several input styles. You can use full axis lengths. You can use semi-axis values. You can also use the semi-major axis with eccentricity or focal distance. This makes the tool practical for algebra, geometry, and coordinate graph problems.

Helpful Output for Students

The result section shows the center, axes, focus points, directrices, vertices, co-vertices, eccentricity, and standard equation. It also gives the latus rectum length. These outputs help students verify homework, prepare notes, and check classroom examples with less effort.

Ideal for Coordinate Geometry Practice

Coordinate geometry often requires careful substitutions. Small mistakes can change the final answer. This calculator reduces repeated manual work and lets learners compare horizontal and vertical ellipses quickly. It is useful for revision, guided practice, quizzes, and self-check activities.

Clean Records for Review

The CSV and PDF export options help organize answers. Students can save worked examples and review them later. Teachers can also use the output for quick demonstrations. A clear report supports better learning and helps track patterns across different ellipse questions.

Frequently Asked Questions

1. What does this calculator find?

It finds focus points, directrices, eccentricity, axis lengths, vertices, co-vertices, latus rectum length, and the standard ellipse equation.

2. What is the difference between a, b, and c?

a is the semi-major axis, b is the semi-minor axis, and c is the distance from the center to each focus.

3. Why must a be larger than b?

For an ellipse in standard form, the semi-major axis is the longest radius. That value is always at least as large as the semi-minor axis.

4. What range can eccentricity have?

Eccentricity for an ellipse must be greater than 0 and less than 1. Values outside that range do not describe an ellipse.

5. How are directrices calculated?

The directrices use a/e. For horizontal ellipses, they are x = h ± a/e. For vertical ellipses, they are y = k ± a/e.

6. Can I use axis lengths instead of semi-axis values?

Yes. The tool accepts full major and minor axis lengths. It converts them into semi-axis values before calculating the ellipse properties.

7. Does the center affect focus and directrix values?

Yes. The center shifts every coordinate result. The curve shape stays the same, but the final positions move according to h and k.

8. Why download CSV or PDF reports?

Downloads help save worked examples, compare practice questions, submit notes, and keep a simple record of important ellipse calculations.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.