Chapter 1: Problem 7
In Exercises \(5-12,\) sketch the graph of the equation by translating, reflecting, compressing. and stretching the graph of \(y=x^{2}\) appropriately. and then use a graphing utility to confirm that your sketch is correct. $$y=-2(x+1)^{2}-3$$
Short Answer
Expert verified
The graph is a downward-opening parabola with vertex (-1,-3), vertically compressed by 2.
Step by step solution
01
Identify Base Graph
The base graph is the function \( y = x^2 \), which is a parabola opening upwards with its vertex at the origin (0,0).
02
Horizontal Translation
The term \((x+1)^2\) indicates a horizontal shift. Since \(x\) is replaced with \(x+1\), the graph shifts to the left by 1 unit. The new vertex becomes (-1,0).
03
Vertical Compression and Reflection
The coefficient \(-2\) in \(-2(x + 1)^2\) both compresses the graph vertically and reflects it across the x-axis. The parabola is now upside down (opens downward) and twice as steep. The vertex remains at (-1,0) but the graph is narrower and inverted.
04
Vertical Translation
Finally, the \(-3\) at the end of the equation \(-2(x+1)^2 - 3\) shifts the entire graph down by 3 units. The vertex is now at (-1,-3).
05
Sketch the Graph
Using the transformations identified, sketch the parabola on a coordinate plane. Start at the new vertex (-1,-3), plot additional points if necessary, and ensure it opens downward and is narrower than \( y = x^2\).
06
Confirm with Graphing Utility
Use a graphing utility to plot the equation \( y = -2(x+1)^2 - 3 \) to confirm the accuracy of your sketch. The graph on the utility should match your drawing.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Parabola
A parabola is a U-shaped curve that is the graph of a quadratic function. The standard form of a parabola is given by the equation \(y = ax^2+bx+c\). In its simplest form, such as \(y=x^2\), the parabola is symmetrical and opens upwards with its vertex located at the origin, (0,0).
- **Vertex:** The highest or lowest point of the parabola, depending on its orientation.
- **Axis of Symmetry:** A vertical line through the vertex, dividing the parabola into two mirror-image halves.
- **Direction of Opening:** Determined by the sign of \(a\). If \(a > 0\), it opens upwards; if \(a < 0\), it opens downwards.
Horizontal Translation
Horizontal translation involves shifting the graph left or right. In the equation \((x+1)^2\), \(x\) is replaced by \(x+1\), indicating a shift.
When the form involves \((x+k)^2\), where \(k\) is a constant, the graph moves left by \(k\) units if \(k > 0\) and right if \(k < 0\).
For our problem:
When the form involves \((x+k)^2\), where \(k\) is a constant, the graph moves left by \(k\) units if \(k > 0\) and right if \(k < 0\).
For our problem:
- Since we have \((x+1)^2\), \(k = 1\), so the graph shifts left by 1 unit.
- The new vertex from the origin becomes (-1,0).
Vertical Compression
Vertical compression changes the steepness of the parabola. It is impacted by multiplying the quadratic term by a coefficient. In the function \(-2(x + 1)^2\), the coefficient is \(-2\).
This coefficient does double duty:
This coefficient does double duty:
- **Compression:** The factor of 2 narrows the parabola, making it steeper than the standard \(y=x^2\).
- **Reflection:** The negative sign reflects the parabola downwards.
Vertical Translation
Vertical translation involves moving the entire graph up or down along the y-axis. It is dictated by adding or subtracting a constant to the equation. In \(-2(x+1)^2-3\), the term \(-3\) is responsible for this shift.
Here's how it works:
Here's how it works:
- **Translation Down:** The subtraction of 3 moves the entire graph down by 3 units.
- The vertex, previously at (-1,0), is now repositioned to (-1,-3).