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http://prntscr.com/mfihwy

 Feb 2, 2019
 #1
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The directrix lies below the focus...so...this parabola turns upward....we can immediately rule out the last two answers

 

The vertex lies at (0, (-3 - 2) /2) =   (0, -5/2)

 

We have the form

 

4p ( y - k) =  (x -h)^2        where (h, k) is the vertex = (0, -5/2)

 

p is the distance between the focus and vertex = 1/2 units

 

So we have

 

4(1/2)(y - [- 5/2] ) = (x - 0)^2

 

2(y + 5/2) = x^2

 

2y + 5 = x ^2

 

2y = x^2 - 5      divide both sides by 2

 

y = (1/2)x^2 - 5/2

 

 

cool cool cool

 Feb 2, 2019

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