# Product of distances from foci to any tangent of an ellipse

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• ElectronicTeaCup
In summary, the conversation discusses the difficulty of algebraic manipulations in a self-study Calculus course and whether it is acceptable to peek at the answer and force the solving into the direction of the solution. The importance of practicing algebra and the potential mistakes that can arise are also mentioned. Finally, the use of LaTeX to write equations is recommended and a correction is made to an equation in the conversation.
ElectronicTeaCup
TL;DR Summary
Show that the product of the distances from the foci to any point of any tangent to an ellipse is ##b^2##
where b is the semi-minor axis.
As part of the final stage of a problem, there is some algebraic manipulation to be done (from the solution manual):

But I'm getting lost somewhere:

Also a bit of general advice needed: This is part of a self-study Calculus course, and I often have difficulty with bigger algebraic manipulations like this. I often feel if I made a deviation at some point, I will never be able to get to the solution—and I am assuming I need to go through all the possible ways before I have my solution. When in such a situation, I peek at the answer and force the solving into the direction of the solution. Is this bad practice? I feel I shouldn't be spending inordinate amounts of time on algebra in a calculus course.

As written, the statement is clearly wrong. Every point outside the ellipse is element of two tangents, including points that are 1000 b away from the ellipse. What they mean is the distance between the foci and the tangent, not arbitrary points on the tangent.

I don't understand how you get from your first image to the first equation in the second image. Did you swap c <-> c2? It's usually better to simplify first before you plug in things that make the equations longer.
Getting algebra right is an important skill everywhere, so practicing it is a good idea. There are many ways to get to the solution, but a wrong step somewhere will throw off the approach every time. Sometimes it's clear from the wrong answer where things went wrong, sometimes it is not.

You can use LaTeX to write equations here, by the way:
$$\frac{a^2b^2x_0}{b^2+c^2}$$

ElectronicTeaCup
Thank you for your reply. I notice now that not only did I write the equation incorrectly, (wrote ##b^{4} x_{0}## instead of ##b^{4} x^2_{0}##) I incorrectly substituted ##c^2## for ##c##

Thank you for your advice, I have this misconception that algebra is unimportant in the computer age and keep avoiding algebraic mistakes by abandoning questions that involve any algebra I find difficult. I will do better, and stick to it.

## 1. What is the definition of "Product of distances from foci to any tangent of an ellipse"?

The product of distances from foci to any tangent of an ellipse is a mathematical concept that represents the multiplication of the distances from the two foci of an ellipse to any tangent line drawn to the ellipse. It is a constant value for a given ellipse.

## 2. How is the product of distances from foci to any tangent of an ellipse calculated?

The product of distances from foci to any tangent of an ellipse can be calculated using the formula P = 2ab, where a and b are the semi-major and semi-minor axes of the ellipse, respectively.

## 3. What is the significance of the product of distances from foci to any tangent of an ellipse?

This value is important in the study of ellipses and conic sections as it is used to determine the eccentricity of an ellipse. It also has applications in optics and engineering, particularly in the design of reflective and refractive surfaces.

## 4. Can the product of distances from foci to any tangent of an ellipse be negative?

No, the product of distances from foci to any tangent of an ellipse is always positive. This is because distances are always positive values and the product of two positive values is also positive.

## 5. Is the product of distances from foci to any tangent of an ellipse the same for all ellipses?

No, the product of distances from foci to any tangent of an ellipse varies for different ellipses. It is dependent on the size and shape of the ellipse, as well as the location of the foci.

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