Geometry

Question Analysis  

The main focus is to determine the directrix of a horizontal parabola given its equation. We need to identify the vertex and focal length by rewriting the equation in standard form.  

 

Key Concept Explanation  

Horizontal Parabola Standard Form: For , the vertex is . The directrix is a vertical line:  

If a > 0 (opens right), directrix: .  

If a < 0 (opens left), directrix: .  

 

Step-by-Step Solution  

1. Identify parameters:  

Given , compare to :  

, , (vertex: ).  

2. Calculate focal distance:  

.  

3. Determine directrix:  

Since a < 0 (opens left), the directrix is units to the right of the vertex:  

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