Chapter 8: Problem 32
Graph the function, label the vertex, and draw the axis of symmetry. $$ f(x)=-3(x+7)^{2} $$
Short Answer
Expert verified
Vertex: (-7, 0); Axis of Symmetry: x = -7
Step by step solution
01
Identify the Parabola Form
The given function is already in vertex form, which is \[f(x) = a(x-h)^2 + k\]where \(a = -3\), \(h = -7\), and \(k = 0\). This tells us our parabola opens downwards due to the negative leading coefficient.
02
Determine the Vertex
The vertex of the parabola in vertex form \(f(x) = a(x-h)^2 + k\) is given by the point \((h, k)\). So, the vertex here is \((-7, 0)\).
03
Draw the Axis of Symmetry
The axis of symmetry for a parabolic function of the form \(f(x) = a(x-h)^2 + k\) is the vertical line \(x = h\). Therefore, for the given function, the axis of symmetry is \(x = -7\). Draw a vertical line through \(x = -7\).
04
Plot the Vertex
On a coordinate plane, plot the vertex at the point \((-7, 0)\).
05
Sketch the Parabola
Since \(a = -3\) is negative, the parabola opens downwards. From the vertex \((-7, 0)\), draw a symmetric U-shaped curve opening down.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
vertex form of a parabola
Understanding the vertex form of a parabola is key to graphing quadratic functions. The vertex form is given by \(f(x) = a(x-h)^2 + k\). In this form, \(h\) and \(k\) are the coordinates of the vertex of the parabola. The value \(a\) determines the direction and the width of the parabola:
- If \(a > 0\), the parabola opens upwards.
- If \(a < 0\), the parabola opens downwards.
- The larger the absolute value of \(a\), the narrower the parabola.
axis of symmetry
The axis of symmetry is a vertical line that runs through the vertex of the parabola, dividing it into two mirror-image halves. For the vertex form \(f(x) = a(x-h)^2 + k\), the axis of symmetry has the equation \(x = h\). Because this line is vertical, it is expressed as \(x = \text{constant}\).
In the given function \(f(x)=-3(x+7)^2\), \(h = -7\). Therefore, the axis of symmetry is the line \(x = -7\). This vertical line helps in plotting symmetrical points on either side of the parabola.
In the given function \(f(x)=-3(x+7)^2\), \(h = -7\). Therefore, the axis of symmetry is the line \(x = -7\). This vertical line helps in plotting symmetrical points on either side of the parabola.
plotting parabolas
To graph a parabola, start by plotting the vertex, which is the most central point. Here, for \(f(x)=-3(x+7)^2\), the vertex is \(-7,0\). Mark this point on the graph.
Next, draw the axis of symmetry \(x=-7\) as a dashed vertical line. This helps in creating a balanced graph.
From the vertex, plot additional points by choosing \(x\)-values on either side, calculating their corresponding \(y\)-values, and ensuring they mirror each other across the axis of symmetry. Finally, draw a smooth, U-shaped curve through these points to complete the parabola. Remember, since \(a\) is negative, this parabola will open downwards.
Next, draw the axis of symmetry \(x=-7\) as a dashed vertical line. This helps in creating a balanced graph.
From the vertex, plot additional points by choosing \(x\)-values on either side, calculating their corresponding \(y\)-values, and ensuring they mirror each other across the axis of symmetry. Finally, draw a smooth, U-shaped curve through these points to complete the parabola. Remember, since \(a\) is negative, this parabola will open downwards.
understanding vertical shifts
Vertical shifts in the vertex form \(f(x) = a(x-h)^2 + k\) can change the position of the parabola along the y-axis. The value of \(k\) determines how far and in which direction the graph shifts vertically:
- If \(k > 0\), the parabola shifts up.
- If \(k < 0\), the parabola shifts down.