(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

An ellipse is a set of all points from two points called a focus (together a foci) has the sum of 2a

|d_{1}+ d_{2}| = 2a

A hyperbola is the same except it is difference.

Now my question is, just who came up with these definitions that it must equal to 2a?? Because if I don't remember that it is 2a, then I will never be able to understand the formulas.

3. The attempt at a solution

attempedt at daydreaming an answer, but failed.

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# Hyperbola and Ellipse's definition

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