Chapter 11: Problem 39
Graph each parabola. Give the vertex, axis of symmetry, domain, and range. $$ x=3 y^{2}+12 y+5 $$
Short Answer
Expert verified
Vertex: (2, -3). Axis of Symmetry: \(x = 2\). Domain: \(\{x \in \mathbb{R}\}\). Range: \(\{y \geq -3\}\).
Step by step solution
01
Identify the Vertex
The given equation is in vertex form, which is \[ f(x) = a(x-h)^2 + k \] for a parabola. Here, \(a = \frac{1}{2} \), \(h = 2\), and \(k = -3\). So, the vertex is at the point (h, k) = (2, -3).
02
Determine the Axis of Symmetry
The axis of symmetry for a parabola in vertex form \(f(x) = a(x-h)^2 + k\) is always the vertical line \(x = h\). Therefore, the axis of symmetry is \(x = 2\).
03
Determine the Domain
The domain of any parabola is all real numbers because a parabola extends infinitely in both the left and right directions. So, the domain is \(\{x \in \mathbb{R}\}\).
04
Determine the Range
Since \(a > 0\) (\(a = \frac{1}{2}\) in this case), the parabola opens upwards. The lowest point on this parabola is the vertex \( (2, -3)\). Therefore, the range is all real numbers greater than or equal to -3, represented as \(\{y | y \geq -3\}\).
05
Sketch the Graph
Using the vertex \((2, -3)\), plot the point on a coordinate plane. Draw the axis of symmetry, which is the vertical line \(x = 2\). Since the parabola opens upwards and is wider than the standard \(y = x^2\) parabola (because \(a = \frac{1}{2} < 1\)), draw the parabola opening up from the vertex point.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
vertex form
When graphing a parabola, one of the easiest forms to work with is the vertex form. This form is written as \( f(x) = a(x-h)^2 + k \). Here, \( (h, k) \) represents the vertex of the parabola, and \( a \) determines the width and direction of the parabola's opening.
In our example equation \( f(x) = \frac{1}{2}(x-2)^2 -3 \):
Working with the vertex form allows you to directly read the vertex, making it simpler to start your graph.
In our example equation \( f(x) = \frac{1}{2}(x-2)^2 -3 \):
- \( h = 2 \)
- \( k = -3 \)
Working with the vertex form allows you to directly read the vertex, making it simpler to start your graph.
axis of symmetry
The axis of symmetry is a vertical line that passes through the vertex of the parabola. It divides the parabola into two mirror-image halves. For parabolas written in vertex form \( f(x) = a(x-h)^2 + k \), the axis of symmetry is always the line \( x = h \).
In our example:
Our equation is \( f(x) = \frac{1}{2}(x-2)^2 -3 \), so:
Knowing the axis of symmetry helps in plotting the parabola accurately.
In our example:
Our equation is \( f(x) = \frac{1}{2}(x-2)^2 -3 \), so:
- \( h = 2 \)
Knowing the axis of symmetry helps in plotting the parabola accurately.
domain and range
Understanding the domain and range of a parabola is key to knowing where the graph extends. The domain of a parabola covers all possible x-values it can take. Since parabolas stretch infinitely left and right, the domain is always all real numbers, or \( \{x \, | \, x \in \, \mathbb{R}\} \).
For the range, it depends on whether the parabola opens upwards or downwards. This is determined by the parameter \( a \):
\( \{y \, | \, y \geq -3\} \).
For the range, it depends on whether the parabola opens upwards or downwards. This is determined by the parameter \( a \):
- If \( a > 0 \), the parabola opens upwards
- If \( a < 0 \), it opens downwards
\( \{y \, | \, y \geq -3\} \).
parabola graph
Graphing a parabola involves several steps to ensure accuracy. We'll use our example equation \( f(x) = \frac{1}{2}(x-2)^2 -3 \):
- Start with plotting the vertex at \( (2, -3) \).
- Draw the axis of symmetry, a vertical line at \( x = 2 \).
- Since the parabola opens upwards and \( a = \frac{1}{2} \), it is wider than the standard parabola.
- Choose additional points to plot, like those to the left and right of the vertex, and mirror them across the axis of symmetry.
- Draw the curve through these points.