Chapter 1: Problem 18
Use your graphing calculator to graph \(y=a x^{2}\) for \(a=\frac{1}{5}, 1\), and 5 , then again for \(a=-\frac{1}{5},-1\), and \(-5\). Copy all six graphs onto a single coordinate system and label each one. Explain how a negative value of \(a\) affects the parabola.
Short Answer
Expert verified
A negative value of \( a \) causes the parabola to open downward.
Step by step solution
01
Understand the Quadratic Function
We are working with the quadratic function \( y = ax^2 \), where the coefficient \( a \) determines the shape and orientation of the parabola. We will graph this function for different values of \( a \).
02
Graphing Positive Values of 'a'
Use your calculator to graph the function for positive values of \( a \): - For \( a = \frac{1}{5} \), the graph is a wide upward-opening parabola.- For \( a = 1 \), the graph is a standard upward-opening parabola.- For \( a = 5 \), the graph is a narrow upward-opening parabola.Plot these three graphs on the same coordinate system, labeling each one accordingly.
03
Graphing Negative Values of 'a'
Now graph the function for negative values of \( a \):- For \( a = -\frac{1}{5} \), the graph is a wide downward-opening parabola.- For \( a = -1 \), the graph is a standard downward-opening parabola.- For \( a = -5 \), the graph is a narrow downward-opening parabola.Plot these three graphs on the same coordinate system, labeling each one accordingly.
04
Analyze the Effect of Negative 'a'
When \( a \) is negative, the parabola opens downward instead of upward. The absolute value of \( a \) determines how wide or narrow the parabola appears, without affecting the direction of the opening.
05
Copy All Graphs onto a Single Coordinate System
Ensure all six parabolas are plotted on the same coordinate system. Label each parabola with its respective value of \( a \). This visual representation helps compare the effects of different \( a \) values, both positive and negative.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Parabolas
Parabolas are U-shaped curves that are graphically represented by quadratic functions. When graphed, the basic form of a parabola is expressed as \( y = ax^2 \). The value of \( a \) influences certain characteristics of the parabola, such as its width and direction of opening. In general:
- If \( a > 0 \), the parabola opens upward, resembling a smile.
- If \( a < 0 \), the parabola opens downward, resembling a frown.
Quadratic Function Characteristics
Quadratic functions, typically expressed in the form \( y = ax^2 + bx + c \), have distinct characteristics. However, examining the simpler form \( y = ax^2 \) sheds light on fundamental attributes:
- Vertex: This is the highest or lowest point of the parabola, depending on its orientation. For \( y = ax^2 \), the vertex is located at the origin, \( (0,0) \).
- Axis of Symmetry: Parabolas are symmetrical about a vertical line called the axis of symmetry. In our case, it's the y-axis, or \( x = 0 \).
- Direction of Opening: As mentioned, the sign of \( a \) determines whether it opens upwards or downwards.
- Width: The absolute value of \( a \) affects the width. Smaller values result in wider parabolas, while larger values cause narrower ones.
Effects of Coefficient on Graph Shape
The coefficient \( a \) in the equation \( y = ax^2 \) holds significant sway over the graph's appearance. Here’s a breakdown of how \( a \) affects the parabola:
- Positive & Negative Values of \( a \): As previously noted, positive values of \( a \) yield upwards-opening parabolas, while negative values flip the parabola to open downwards.
- Magnitude of \( a \): The width of the parabola is contingent on \( |a| \), the absolute value of \( a \). The smaller \( |a| \) is, the wider the parabola becomes; conversely, as \( |a| \) increases, the parabola becomes narrower.