Given the equation (x + 4)^2 = -12y + 24 determine: a)  The Vertex b)  If the parabola opens up, down, left, right c)  The Focus



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Posted on (Answer #1)


(a) Vertex

To determine the vertex, express the given equation of the parabola to its vertex form which is:


where (h,k) is the vertex.

To convert the equation in this form, subtract both sides by 24.



And divide both sides by -12.



So the vertex form of the given equation is:


Hence, the vertex of the parabola is `(-4,2)` .

(b) Direction of the parabola.

Note that when it is the variable x that is squared, the parabola either opens up or down.

And if it is the variable y that is squared, the parabola either opens to the left or right.

In the given equation, it is the variable x that is squared. So, it is either upward or downward. To determine which of these two is the direction of the parabola, consider the value of a.

If a is positive, the parabola opens up. And if it is negative, it open down.

Base on the vertex form, `a=-1/12` . 

Since a is negative, therefore, the parabola opens down.

(C) Focus

Since the parabola is downward, then its axis of symmetry is vertical. And a parabola with vertical axis, its focus has a coordinates (h, k+p).

To solve for p, use the formula:


Since a=-1/12, the value of p will be:




Then, substitute h=-4, k=2 and p=-3 to the coordinate form of the focus.


Hence, the focus of the parabola is `(-4 , -1)` .

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