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A parabola, with its vertex at the origin, has a directrix at [tex]\( y = 3 \)[/tex].

Which statements about the parabola are true? Select two options.

A. The focus is located at [tex]\( (0, -3) \)[/tex].
B. The parabola opens to the left.
C. The [tex]\( p \)[/tex] value can be determined by computing [tex]\( 4(3) \)[/tex].
D. The parabola can be represented by the equation [tex]\( x^2 = -12y \)[/tex].
E. The parabola can be represented by the equation [tex]\( y^2 = 12x \)[/tex].

Sagot :

To solve the problem, let's follow a step-by-step approach:

1. Understanding the Vertex and Directrix:
- The given parabola has its vertex at the origin, which is [tex]\((0, 0)\)[/tex].
- The directrix of the parabola is given as [tex]\(y = 3\)[/tex].

2. Identifying the Direction of Opening:
- Given that the directrix ([tex]\(y = 3\)[/tex]) is above the vertex ([tex]\(0, 0\)[/tex]), the parabola must open downwards.

3. Determining the Parameters of the Parabola:
- For a parabola that opens vertically (either upwards or downwards), the general form of the equation is [tex]\((x - h)^2 = 4p(y - k)\)[/tex], where [tex]\((h, k)\)[/tex] is the vertex and [tex]\(p\)[/tex] is the distance from the vertex to the focus (and also the distance from the vertex to the directrix, but in the opposite direction).
- Here, the vertex is at [tex]\((0, 0)\)[/tex], so [tex]\(h = 0\)[/tex] and [tex]\(k = 0\)[/tex].
- The directrix is at [tex]\(y = 3\)[/tex]. The distance [tex]\(p\)[/tex] from the vertex to the directrix is thus [tex]\(p = 3\)[/tex].

4. Focus of the Parabola:
- Since the parabola opens downwards, the focus lies below the vertex at a distance of [tex]\(p = 3\)[/tex].
- Therefore, the focus of the parabola is at [tex]\((0, -3)\)[/tex].

5. Equation of the Parabola:
- Substituting [tex]\(p = 3\)[/tex] into the general form equation:
[tex]\[ (x - 0)^2 = 4 \cdot 3 \cdot (y - 0) \implies x^2 = 12y \][/tex]
- Since the parabola opens downwards, the equation should reflect this by having a negative value:
[tex]\[ x^2 = -12y \][/tex]

By following these steps, we can conclude that the two correct statements about the parabola are:
1. The focus is located at [tex]\((0, -3)\)[/tex].
2. The parabola can be represented by the equation [tex]\(x^2 = -12y\)[/tex].

Thus, our final answer is:
- The focus is located at (0, -3).
- The parabola can be represented by the equation [tex]\(x^2 = -12 y\)[/tex].