Chapter 13: Problem 15
If \(f(x)=|x-1|\) and \(g(x)=f\\{f[f(x)]\\}\), then for \(x>2\), \(g^{\prime}(x)\) is equal to (A) \(-1\) if \(2 \leq x<3\) (B) 1 if \(2 \leq x<3\) (C) 1 for all \(x>2\) (D) None of these
Short Answer
Expert verified
For \( x > 2 \), \( g'(x) = 1 \), so (C) is correct.
Step by step solution
01
Understand the Function Definitions
We start by analyzing the given functions. The function \( f(x) = |x-1| \) represents the absolute value function, which returns the positive difference between \( x \) and 1. This means \( f(x) = x - 1 \) for \( x \geq 1 \) and \( f(x) = 1 - x \) for \( x < 1 \). For \( g(x) = f\{f[f(x)]\} \), it indicates the repeated application of the absolute function three times.
02
Evaluate f(x) for x > 2
For \( x > 2 \), we have \( f(x) = |x - 1| = x - 1 \) since \( x \geq 1 \), ensuring that the expression inside the absolute value is non-negative. Hence, when \( x > 2 \), simplifying \( f(x) \) gives \( x - 1 \).
03
Evaluate f(f(x)) for x > 2
Given \( f(x) = x - 1 \) for \( x > 2 \), we evaluate \( f(f(x)) = f(x - 1) = |(x - 1) - 1| = |x - 2| \). Because \( x > 2 \), we have \( x - 2 > 0 \) and thus, \( f(f(x)) = x - 2 \).
04
Evaluate f(f(f(x))) for x > 2
Next, we find \( f(f(f(x))) = f(x - 2) \). This results in \( |x - 2 - 1| = |x - 3| \). For \( x > 2 \), \( x - 3 \) could be negative or positive, but since \( x > 3 \), it will be positive: \( x - 3 \). Hence, \( f(f(f(x))) = x - 3 \) for \( x > 3 \).
05
Differentiate g(x) with respect to x for x > 3
Next, we differentiate \( g(x) = x - 3 \) with respect to \( x \). The derivative of a linear function \( ax + b \) is simply \( a \). So, \( g'(x) = 1 \).
06
Conclusion on g'(x) for x > 2
Given the piecewise nature of the differentiation depending on \( x \), for \( x > 3 \), we found \( g'(x) = 1 \). Therefore, for \( x > 2 \) with \( x > 3 \) in focus, the answer aligns most closely with (C) since it's constant and doesn't switch signs within \( x > 2 \), but we focus here on where the differentiable portion applies.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Absolute Value Function
The absolute value function is a fundamental concept in calculus and mathematics. It represents the distance a number is from zero on the number line, ignoring its direction. The notation for absolute value is expressed as \(|x|\), where \(x\) can be any real number.
When working with absolute values, consider the following properties:
Depending on the input \(x\):
When working with absolute values, consider the following properties:
- If \(x\) is positive or zero, \(|x| = x\).
- If \(x\) is negative, \(|x| = -x\).
Depending on the input \(x\):
- If \(x \geq 1\), then \(f(x) = x - 1\).
- If \(x < 1\), then \(f(x) = 1 - x\).
Piecewise Function
A piecewise function is one that is defined using different expressions based on the input value domain. In simpler terms, it consists of "pieces" of different functions. Each piece applies to a specific interval of input values.
To illustrate with our exercise:
To illustrate with our exercise:
- For \(f(x) = |x - 1|\), the function is defined by two linear expressions depending on whether \(x\) is greater than or equal to 1, or less than 1.
- Apply each piece of the function based on the interval of \(x\).
- Reevaluate the sub-functions using piecewise definitions at each step.
Differentiation
Differentiation is a core concept in calculus, focusing on finding the rate at which function values change concerning changes in their input. Simply put, it helps us understand how the output of a function grows or diminishes as its input moves.
To differentiate a function manually, you apply derivative rules, such as:
To differentiate a function manually, you apply derivative rules, such as:
- The power rule: If \(f(x) = x^n\), then \(f'(x) = nx^{n-1}\).
- The constant rule: The derivative of a constant is zero.
- The sum rule: The derivative of the sum is the sum of the derivatives.
- The derivative \(g'(x)\) is 1, since the slope of the linear function is the coefficient of \(x\).