SOLUTION: Write the equation of the directrix of the conic section shown below. Write your answer without using spaces. x^2+6x-4y+5=0 Thank you.

Algebra ->  Quadratic-relations-and-conic-sections -> SOLUTION: Write the equation of the directrix of the conic section shown below. Write your answer without using spaces. x^2+6x-4y+5=0 Thank you.      Log On


   

Question 1100797: Write the equation of the directrix of the conic section shown below. Write your answer without using spaces. x^2+6x-4y+5=0
Thank you.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Get the parabola into focus form by completing the square,
x%5E2%2B6x%2B5=4y
%28x%5E2%2B6x%2B9%29%2B5=4y%2B9
%28x%2B3%29%5E2=4y%2B4
%28x%2B3%29%5E2=4%28y%2B1%29
Compared to the focus form,
%28x-h%29%5E2=4p%28y-k%29
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(-3,-1) is the vertex.
4p=4
p=1
So the focus is (-3,-1)+(0,1)=(-3,0).
The directrix is then,
y=-2
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