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| 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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