Chapter 4: Problem 16
Identify the coordinates of any local and absolute extreme points and inflection points. Graph the function. $$y=1-(x+1)^{3}$$
Short Answer
Expert verified
The local and absolute extremum and inflection point is at (-1, 1).
Step by step solution
01
Identify the Function
The given function is \( y = 1 - (x+1)^3 \). This is a cubic function.
02
Find the First Derivative
To find the critical points, we first find the derivative of the function. The derivative is determined using the chain rule:\[y' = \frac{d}{dx}[1 - (x+1)^3] = -3(x+1)^2\]
03
Set the First Derivative to Zero
Find the critical points by solving \( y' = 0 \):\[-3(x+1)^2 = 0\]This simplifies to \[(x+1)^2 = 0\]Solving for \(x\), we get one solution:\[x = -1\]
04
Determine the Second Derivative
To find inflection points, calculate the second derivative:\[y'' = \frac{d}{dx}[-3(x+1)^2] = -6(x+1)\]
05
Set the Second Derivative to Zero
Solve for potential inflection points by setting \( y'' = 0 \):\[-6(x+1) = 0\]Solving for \(x\), we have:\[x = -1\]
06
Evaluate the Coordinates of Critical and Inflection Points
Substitute \(x = -1\) into the original equation to find the y-coordinate:\[y = 1 - (-1+1)^3 = 1 - 0 = 1\]So the coordinates of both the local/absolute extremum and inflection point are \((-1, 1)\).
07
Graphing the Function
The graph of the function \( y = 1 - (x+1)^3 \) is a downward-shifted cubic curve. The point \((-1, 1)\) is both an extremum and an inflection point, meaning the graph changes concavity at this point.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Critical Points
Critical points are essential in understanding a function's behavior, especially for identifying the locations of maximum or minimum values. To find critical points of a function, we perform the following steps:
- First, calculate the first derivative of the function. The first derivative, denoted as \(y'\), helps us determine the rate of change of the function.
- Set the first derivative equal to zero. Solving \(y' = 0\) enables us to find the values of \(x\) where the slope of the tangent to the function is zero. These are the candidate points for maximum or minimum values.
- In the case of \(y = 1 - (x+1)^3\), the first derivative is \(y' = -3(x+1)^2\). Setting this to zero, we only find one critical point at \(x = -1\). This means \(x = -1\) is potentially where the function may have a "peak" or "valley".
Inflection Points
Inflection points are where a function changes its concavity, which means it transitions from concave up to concave down or vice versa. The steps to find inflection points are as follows:
- Calculate the second derivative of the function. The second derivative, denoted as \(y''\), helps us understand how the rate of change itself changes.
- Set the second derivative equal to zero to find possible inflection points. Solving \(y'' = 0\) gives the values of \(x\) where inflection points can occur.
- For the function \(y = 1 - (x+1)^3\), we find \(y'' = -6(x+1)\), which equals zero at \(x = -1\). This implies the function might change concavity at this point.
Derivatives
Understanding derivatives is crucial for analyzing cubic functions, as they help us explore the function's behavior.
The **first derivative** \(y'\) of a function allows us to examine the function's slope, indicating where it rises or falls:
The **first derivative** \(y'\) of a function allows us to examine the function's slope, indicating where it rises or falls:
- Using the chain rule, the derivative of \(y = 1 - (x+1)^3\) becomes \(y' = -3(x+1)^2\).
- This provides us with a tool to find points where the function's rate of change is zero (i.e., critical points).
- The second derivative is calculated from the first derivative. Here, \(y'' = -6(x+1)\), which helps us identify possible inflection points.
- It tells us where the graph changes its concavity and further reveals the function's complexity.
Graphing Functions
Graphing functions is a visual approach to understanding how mathematical equations behave in different intervals.
To graph a function:
To graph a function:
- Identify critical points and inflection points. Here, for \(y = 1 - (x+1)^3\), critical and inflection points are both at \((-1, 1)\).
- Evaluate the end behavior. For our cubic function, as \(x\) approaches infinity, the \(y\)-values decrease due to the \(-x^3\) nature of the expression.
- Sketch the curve, especially noting the behavior around critical points and inflection points. Since \((-1, 1)\) acts both as an extremum and an inflection point, the graph transitions between concave up and concave down here.