QUESTION IMAGE
Question
- determine the vertex and the direction in which the parabola $x^{2}=-8z$ opens.
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- determine the vertex and the direction in which the parabola $y^{2}=12x$ opens.
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- determine the vertex and the direction in which the parabola $(z - 3)^{2}=4(y + 1)$ opens.
vertex
direction
- determine the vertex and the direction in which the parabola $(y + 2)^{2}=-6(z - 4)$ opens.
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direction
Step1: Recall parabola vertex - form
The standard - form of a parabola is either $(y - k)^2=4p(x - h)$ (opens left or right) or $(x - h)^2 = 4p(y - k)$ (opens up or down), where $(h,k)$ is the vertex.
Step2: Analyze $x^{2}=-8x$
Rewrite it as $x^{2}+8x = 0$. Completing the square: $x^{2}+8x + 16=16$, i.e., $(x + 4)^{2}=16$. In the form $(x - h)^2=4p(y - k)$, here $y = 0$, $h=-4$, $k = 0$, $4p=-8$ so $p=-2$.
The vertex is $(0,0)$ and since $p=-2<0$, it opens to the left.
Step3: Analyze $y^{2}=12x$
In the form $(y - k)^2=4p(x - h)$, $h = 0$, $k = 0$, and $4p=12$, so $p = 3$.
The vertex is $(0,0)$ and since $p = 3>0$, it opens to the right.
Step4: Analyze $(x - 3)^{2}=4(y + 1)$
Comparing with $(x - h)^2=4p(y - k)$, we have $h = 3$, $k=-1$, $p = 1$.
The vertex is $(3,-1)$ and since $p = 1>0$, it opens up.
Step5: Analyze $(y + 2)^{2}=-6(x - 4)$
Comparing with $(y - k)^2=4p(x - h)$, we have $h = 4$, $k=-2$, $4p=-6$ so $p=-\frac{3}{2}$.
The vertex is $(4,-2)$ and since $p=-\frac{3}{2}<0$, it opens to the left.
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- Vertex: $(0,0)$; Direction: Left
- Vertex: $(0,0)$; Direction: Right
- Vertex: $(3,-1)$; Direction: Up
- Vertex: $(4,-2)$; Direction: Left