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#1 2005-08-12 22:52:49
- KiWoonG
- Guest
**_ Parametrics _**
Hi,,
i needed help for parametrics,,
here's a sample question,,,
A parabola has parametric equations x=8t and y=4t^2
Find the coordinates of its focus and equation of its directix.
can somebody help me on this??
#2 2005-08-13 00:14:52
- mathsyperson
- Moderator
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Re: **_ Parametrics _**
I'm not sure what you mean by focus and directix, but it's easy enough to convert it into a normal cartesian equation.
x=8t
t=x/8
y=4t²
y=4(x/8)²
y=4(x²/64)
y=x²/16
And from that, you should be able to get any information you want.
Why did the vector cross the road?
It wanted to be normal.
#3 2005-08-26 12:05:22
- ajp3
- Novice
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Re: **_ Parametrics _**
use the focus directrix form of the eqn of a parabola:
x² = 4py (or y² = 4px for the horizontal case); note that p = the distance from the vertex to the focus = the distance from the vertex to the directrix
now, mathsyperson has already done most of the work!
take x² = 16y = 4(4y), so we see p = 4.
this means our parabola (with vertex (0,0) ) has focus (0, 4) and directrix y = -4