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- Nov 24th 2006, 11:39 AM #1

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## Sorry asking for so much help

I have more questions, sorry to bother

they ask me to write the equation in standard form, then find the center and radius x^2+y^2+8x+7= 0

they also ask me to find the vertex, focus and the lenght of the lactus rectum 8y=x^2

and just one last, so sorry to ask for that much help

find the equation of the parabola that has a focus at (-3,4) and directriz y=2

thank you.

- Nov 24th 2006, 09:37 PM #2

- Nov 24th 2006, 09:57 PM #3
Hello,

the general form of your parabola is: . This is a parabola which opens up and has it's vertex at V(0, 0). The focus has the (general) coordinates . With your equation it becomes: .

The lactus rectum is the chord passing through the focus and perpendicular to the (main) axis. With a parabola the lactus rectum has always the length 2p. In your case the lactus rectum is 8.

EB

- Nov 25th 2006, 01:55 AM #4
Hello,

the directriz is below the focus thus the parabola opens upward and the main axis is x = -3.

The midpoint on the main axis between the focus and the directriz is the vertex V(d, c) thus your vertex is V(-3, 3).

The general form of your parabola is:

The distance between focus and directriz is p.

Plug in the values you know:

. Solve for y:

EB

- Nov 25th 2006, 09:30 AM #5

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