Chapter 2: Problem 2
Each of the graphs of the functions has one relative maximum and one relative minimum point. Find these points using the first-derivative test. Use a variation chart as in Example \(1 .\) $$ f(x)=x^{3}-6 x^{2}+1 $$
Short Answer
Expert verified
Relative maximum at (0, 1) and relative minimum at (4, -31).
Step by step solution
01
- Find the first derivative
First, determine the first derivative of the function. Given function is \[ f(x) = x^3 - 6x^2 + 1 \]. Differentiate to find: \[ f'(x) = 3x^2 - 12x \].
02
- Set the first derivative to zero
Solving \[ 3x^2 - 12x = 0 \] for x, factorize the equation: \[ 3x(x - 4) = 0 \]. This gives two critical points: \[ x = 0 \] and \[ x = 4 \].
03
- Create a variation chart
Establish intervals around the critical points to test the sign of \[ f'(x) \]: 1. For \[ -\text{infinity} < x < 0 \] choose \[ x = -1 \], then \[ f'(-1) = 3(-1)^2 - 12(-1) = 3 + 12 = 15 > 0 \]. 2. For \[ 0 < x < 4 \] choose \[ x = 1 \], then \[ f'(1) = 3(1)^2 - 12(1) = 3 - 12 = -9 < 0 \]. 3. For \[ x > 4 \] choose \[ x = 5 \], then \[ f'(5) = 3(5)^2 - 12(5) = 75 - 60 = 15 > 0 \].
04
- Determine the nature of critical points
Combine the signs from the intervals to identify the nature of each critical point: 1. At \[ x = 0 \]: the sign changes from positive to negative, indicating a relative maximum. 2. At \[ x = 4 \]: the sign changes from negative to positive, indicating a relative minimum.
05
- Find the corresponding function values
Evaluate the function \[ f(x) \] at the critical points: \[ f(0) = 0^3 - 6(0)^2 + 1 = 1 \], so relative maximum at \[ (0, 1) \]. And \[ f(4) = 4^3 - 6(4)^2 + 1 = 64 - 96 + 1 = -31 \], so relative minimum at \[ (4, -31) \].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
relative maximum
A relative maximum of a function occurs at a point where the function's value is higher than at any nearby points. It is not necessarily the highest point of the whole function, but it's a 'peak' in its local neighborhood. Find these points using the first-derivative test.
The first-derivative test is an efficient method to find relative maxima and minima:
Finally, calculate the function value at \( x = 0 \) to get the maximum value, which was \( f(0) = 1 \). So, the relative maximum is at \( (0, 1) \).
The first-derivative test is an efficient method to find relative maxima and minima:
- First, find the function's first derivative, denoted as \( f'(x) \). This step will help you understand how the function is changing at every point.
- Next, set \( f'(x) = 0 \). Solve for \( x \) to find critical points where the function could potentially reach a relative maximum or minimum.
- Now, test intervals around each critical point to determine whether the first derivative is positive or negative.
- If the sign of \( f'(x) \) changes from positive to negative around a critical point, it means the function is rising then falling, indicating a relative maximum at that point.
Finally, calculate the function value at \( x = 0 \) to get the maximum value, which was \( f(0) = 1 \). So, the relative maximum is at \( (0, 1) \).
relative minimum
A relative minimum of a function happens at a point where the function's value is lower than at any nearby points. It's a 'valley' in its local area but not necessarily the lowest point of the entire function.
To determine a relative minimum, follow these steps with the first-derivative test:
To determine a relative minimum, follow these steps with the first-derivative test:
- Find the first derivative of the function \( f'(x) \), which tells you where the slopes of the function change.
- Set the first derivative \( f'(x) = 0 \) to locate critical points.
- Check the intervals around each critical point to see if the sign of \( f'(x) \) switches from negative to positive.
- If the sign of \( f'(x) \) changes from negative to positive, this means the function is falling then rising, indicating a relative minimum.
calculus
Calculus is a branch of mathematics focusing on changes and motion. It mainly involves two major concepts: derivatives and integrals. Derivatives help in understanding the rate of change, while integrals help in finding the total accumulation or area under curves.
- The derivative of a function, \( f'(x) \), represents the slope or the rate of change of the function at any given point. It shows how the function’s value is changing at each point.
- Understanding calculus and using tools like the first-derivative test provides a systematic way to analyze functions thoroughly. It’s essential in many scientific disciplines and practical applications.