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Hello I just need a little help, thanks (I did try to answer it so please be nice)

 

What is the equation of a parabola with (−1,−3)  as its focus and y = 1 as its directrix?

My answer-> (x+1)^2-4 

I dont know if I'm right though

Guest May 31, 2017
 #1
avatar+88898 
+1

 

Focus  =  ( -1, - 3)   

 

Directrix  ...   y  =  1

 

The vertex will  lie  at     (-1 ,  [ -3 + 1] / 2 )   = ( -1, -2/2 ) =    ( -1, -1)

 

So, p =  -2  ......and we have

 

4p ( y + 1)  =  (x + 1)^2

 

4 (-2) ( y + 1)  =  ( x + 1)^2

 

-8 ( y + 1)  = (x + 1)^2        multiply through by -1/8

 

y + 1   =  (-1/8)(x + 1)^2      subtract 1 from both sides

 

y  =  -(1/8)(x + 1)^2   -   1

 

 

 

cool cool cool

CPhill  May 31, 2017

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