Quadritic curves, how can foci = vertice?

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SUMMARY

The discussion centers on the properties of quadratic curves, specifically the relationship between the foci and vertices of a parabola. The value of 'a' is established as 3, representing the distance from the center to a vertex, while 'c' is identified as 3√2, the distance from the center to a focus. The confusion arises from the misinterpretation of these distances, clarifying that 'a' does not equate to the distance to the foci. This distinction is crucial for understanding the geometric properties of parabolas.

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Homework Statement




[PLAIN]http://img688.imageshack.us/img688/5336/unledaty.jpg


The Attempt at a Solution



I underlined a = 3, which doesn't make sense seeing the foci is at (plus/minus3, 3)

How can this be?? Wouldn't that make a straight line?
 
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You're confusing distances and points.

a is the distance between the center and a vertex. The vertices are where the blue curve intersects the focal axis. This distance a = 3.

I use the letter c to indicate the distance between the center and a focus. You can see that while one of the foci is (3, 3), the distance c between the center (which is (0, 0)) and this focus is
[itex]3\sqrt{2}[/itex]
, not 3.
 
Oh right okay thanks lol
 

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