Chapter 10: Problem 166
For the following exercises, rewrite the given equation in standard form, and then determine the vertex \((V),\) focus \((F)\), and directrix \((d)\) of the parabola. $$y^{2}-6 y+12 x-3=0$$
Short Answer
Expert verified
Vertex: (1, 3), Focus: (-2, 3), Directrix: x = 4
Step by step solution
01
Identify the equation form
The given equation is \(y^2 - 6y + 12x - 3 = 0\). This needs to be rewritten in standard form for a parabola.
02
Isolate the quadratic term
Reorder the equation to focus on the \(y\) terms: \(y^2 - 6y = -12x + 3\).
03
Complete the square for the \(y\) terms
1. Take \(-6y\), identify the coefficient of \(y\) which is \(-6\), divide by \(2\) to get \(-3\), and square it to get \(9\).2. Add and subtract \(9\) on the left side: \(y^2 - 6y + 9 - 9 = -12x + 3\).
04
Simplify the equation
1. The equation becomes: \((y - 3)^2 - 9 = -12x + 3\).2. Rearrange to get: \((y - 3)^2 = -12x + 12\), or \((y - 3)^2 = -12(x - 1)\).
05
Identify conic form parameters
The standard form of a parabola opening sideways is \((y-k)^2 = 4p(x-h)\), where \((h, k)\) is the vertex.1. Comparing \((y - 3)^2 = -12(x - 1)\) with \((y-k)^2 = 4p(x-h)\), we find: \(h = 1\), \(k = 3\), and \(4p = -12\).
06
Calculate parameters and determine vertex
1. Calculate \(p\): Since \(4p = -12\), we have \(p = -3\).2. Vertex \(V\): \((h, k) = (1, 3)\).
07
Calculate focus and directrix
1. Focus \((F)\): The parabola opens leftward (since \(p < 0\)), located at \((h + p, k) = (1 - 3, 3) = (-2, 3)\).2. Directrix \((d)\): The directrix is the vertical line \(x = h - p = 1 + 3 = 4\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vertex
In the context of parabolas, the vertex is a crucial point that serves as both a peak and a symmetrical anchor. It is essentially the point at which the parabola makes its sharpest turn. For the given equation
This vertex also acts as a y-symmetry line, meaning the parabola mirrors itself around the vertical line that intersects the vertex.
Understanding this concept helps in graphing and interpreting parabolas efficiently.
- We have derived the vertex, denoted as (V), as the ordered pair (h, k).
- This is (1, 3) for our equation.
- The formula (y-k)^2 = 4p(x-h) helps us see that (h, k) = (1, 3).
This vertex also acts as a y-symmetry line, meaning the parabola mirrors itself around the vertical line that intersects the vertex.
Understanding this concept helps in graphing and interpreting parabolas efficiently.
Focus
The focus of a parabola is an internal fixed point and plays a significant role in how the parabola is shaped. In our example:
This equates to (1 - 3, 3) and gives us F = (-2, 3).
The focus of a parabola has the property that any line drawn from a point on the parabola to the focus is equidistant from the directrix, which ensures the unique curve of a parabola.
It serves as a guide to understand the parabola's width and the way branches open.
- The focus (F) is located at (-2, 3).
- Determined by the value of 'p' which is -3. <- As p is the distance between the vertex and the focus along the horizontal line.
- Calculated by adding 'p' to the 'h' value of the vertex (h = 1).
This equates to (1 - 3, 3) and gives us F = (-2, 3).
The focus of a parabola has the property that any line drawn from a point on the parabola to the focus is equidistant from the directrix, which ensures the unique curve of a parabola.
It serves as a guide to understand the parabola's width and the way branches open.
Directrix
The directrix is a line exterior to the parabola that assists in maintaining its geometric integrity. In coordination with the focus:
Since parabolas tend to image somewhere between their focus and directrix,
understanding the directrix helps in mastering the graphical aspect of conics.
The elegance of a parabola lies in this simplicity – maintaining consistent distances between itself, a focus, and a directrix!
- The directrix is positioned such that every point on the parabola equidistant from the directrix and the focus.
- With regards to our equation, the directrix is given by the vertical line x = 4.
- This is calculated using x = h - p, where h = 1 and p = -3, resulting in x = 4.
Since parabolas tend to image somewhere between their focus and directrix,
understanding the directrix helps in mastering the graphical aspect of conics.
The elegance of a parabola lies in this simplicity – maintaining consistent distances between itself, a focus, and a directrix!