Question 193913:  Write an equation of a parabola with a vertex at the origin.
 
 
8. focus (0, 2)  
9. focus (4, 0)  
10. directrix at y = -8 
 Answer by nerdybill(7384)      (Show Source): 
You can  put this solution on YOUR website! 
 
8. focus (0, 2)  
This is a "vertical" parabola, if so, it follows: 
  
. 
Since, the vertex is at the origin: 
(h,k) = (0,0) 
'c' is the distance from the vertex to the focus 
therefore 
c =2 
Now, we plug it in to 
  
  
  
. 
9. focus (4, 0)  
This is a "horizontal" parabola, if so, it follows: 
  
. 
Since, the vertex is at the origin: 
(h,k) = (0,0) 
'c' is the distance from the vertex to the focus 
therefore 
c =4 
. 
Now, we plug it in to 
  
  
  
. 
10. directrix at y = -8 
This is a "vertical" parabola, if so, it follows: 
  
. 
Since, the vertex is at the origin: 
(h,k) = (0,0) 
'c' is the distance from the vertex to the directrix 
therefore 
c =-8 
Now, we plug it in to 
  
  
  
 
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