Latus Rectum Calculator

Before we jump on the equation of the latus rectum (or go straight ahead, we won't stop you), let's take a look at the concept from where it is derived, a conic section.

Conic sections are, in simple terms, the figure described by the intersection of a cone's surface and a plane.

As you can see in the figure above, three shapes can be formed:

• A circle;
• A parabola;
• A hyperbola; or
• An ellipse.

🙋 How do you differentiate between a circle and an ellipse? Or a parabola and a hyperbola? Our circle calc: find c, parabola calculator, and ellipse calculator are here to help you!

But we will only be interested in the parabola, hyperbola, and ellipse. Why? Because they have at least one focus and directrix.

🔎 Every point in a conic section is equidistant to a point (focus) and a directrix (line), both of which can be located anywhere in space.

How does that relate to the latus rectum? Let's see how below.

The latus rectum is the line segment that goes through a focus and is parallel to the directrix of a conic section. It comes from the Latin words 'latus', which means 'side', and 'rectum', which means 'straight'.

The latus rectum endpoints are on the curve, and you can calculate its length and endpoints' coordinates with our latus rectum calculator.

How do you find the endpoints of a segment? Check our endpoint calculator to learn more.

Latus rectum formula

The equation for the latus rectum depends on the shape you wish to calculate it for, and, as such, we will have:

• Latus rectum of a parabola;
• Latus rectum of a hyperbola; and
• Latus rectum of an ellipse.

Let's take a look at the latus rectum formula for each curve.

Let be the distance between the focus and the vertex of a parabola, the latus rectum () formula for a parabola is:

The standard equation for a hyperbola is:

And using the same parameters and , we obtain the latus rectum of a hyperbola:

Similarly, the equation for an ellipse is:

And the latus rectum formula is the same as the hyperbola:

With our latus rectum calculator, you can easily find the endpoints for the latus rectum, or you can go the hard way and solve the equations manually 😅 (it's your choice).

For a parabola with vertex at its endpoints will be located at:

• , if it opens to the right;
• , if it opens to the left;
• , if it opens upward; or
• , if it opens downward.

For a horizontal hyperbola:

• ; and
• .

For a vertical hyperbola:

• ; and
• .

Where is the linear eccentricity of a hyperbola .

And finally, for a horizontal ellipse:

• ; and
• .

And for a vertical ellipse:

• ; and
• .

Where .

Let's see how you can use our latus rectum calculator to find the latus rectum for each shape.

Parabola example

Suppose we have a parabola described by the following quadratic formula:

This is a vertical parabola. Using our latus rectum calculator, we just need to identify each parameter:

1. .
2. .
3. .
4. Plug in the data and the calculator will solve it for you! .

Or, alternatively by hand:

1. This parabola has a vertex at , and its focus is located at .

2. And so, the distance between the two points is .

3. Using the latus rectum of a parabola formula, we multiply the result by 4 to obtain: .

Hyperbola example

We have a hyperbola with the following equation:

This is equal to:

Since the term containing the is positive, this is a horizontal hyperbola.

We identify the parameters:

1. Transverse axis .
2. Conjugate axis .
3. .
4. .
5. We plug in and obtain: .

Ellipse example

Assume we have an ellipse described by:

The parameters are:

1. .
3. .
4. .
5. Resulting in: .