PLEASE HELP!!!! Write the equation of a parabola with vertex (2,-1) and directrix y=-3.
1 answer:
Answer:
y = 1/8(x -2)^2 -1
Step-by-step explanation:
The vertex form of the equation of a parabola can be written as ...
y = (1/(4p))(x -h)^2 +k
for vertex (h, k) and vertex-to-directrix distance p. Here, the vertex has a y-value of -1, and the directrix has a y-value of -3, so the distance between them is -1 -(-3) = 2, and the desired equation with vertex (2, -1) is ...
y = 1/8(x -2)^2 -1
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<em>Comment on the graph</em>
One description of a parabola is that it is the locus of points equidistant from the focus and the directrix. I like to show that a point on the parabola (not the vertex) meets that requirement. That is what the dashed orange lines are for in the diagram. You can easily see that each has length 4.
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