Re: location of foci in ellipse


The Last Danish Pastry wrote:
<conrad@xxxxxxxxxx> wrote in message
news:1168067893.314253.275640@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

The following explanation I don't quite follow:

http://mathforum.org/library/drmath/view/55323.html

The part that I don't follow is their conclusion
that d(Y1, F1) = d(Y2, F2) = a/2

Specifically how they determiend that it is
a divided by 2!

I know they will evaluate to the same value
but why divide by two? What piece of information
tells us that this is so?

We have shown that d(X1,F1)+d(X1,F2) = a
So, d(Y1,F1)+d(Y1,F2) = a

What is there to suggest that d(Y1,F1) + d(Y1,F2)
is true? I don't see how it follows from the observation
that d(X1, F1) + d(X1, F2) = a.

But, d(Y1,F1) = d(Y1,F2)
So, 2*d(Y1,F1) = a
Thus, d(Y1,F1) = a/2


--
conrad

.

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