Chapter 1: Problem 51
Consider the function \(k\) given by $$k(x)=|x-3|+2$$ a) For what \(x\) -value(s) is the function not differentiable? b) Evaluate \(k^{\prime}(0), k^{\prime}(1), k^{\prime}(4),\) and \(k^{\prime}(10)\).
Short Answer
Expert verified
Function is not differentiable at \(x=3\). Derivatives: \(-1, -1, 1, 1\).
Step by step solution
01
Understanding Non-differentiability of Absolute Value Function
The absolute value function \(|x-a|\) is not differentiable at \(x = a\). Here, the function \(k(x) = |x-3| + 2\) involves an absolute value term where \(a = 3\). Thus, the function \(k(x)\) is not differentiable at \(x = 3\) because the absolute value function has a sharp corner at this point.
02
Calculating Derivatives for Different Intervals
To evaluate the derivatives at given points, first consider the piecewise nature of \(k(x) = |x-3| + 2\). We split it into two cases: 1. If \(x \geq 3\), then \(|x-3| = x-3\), so \(k(x) = x-1\), and its derivative \(k'(x) = 1\).2. If \(x < 3\), then \(|x-3| = 3-x\), so \(k(x) = 5-x\), and its derivative \(k'(x) = -1\).
03
Evaluating Derivatives at Specific Points
Evaluate the derivative \(k'(x)\) at the points given:- For \(x = 0\): Since \(0 < 3\), use \(k'(x) = -1\). So, \(k'(0) = -1\).- For \(x = 1\): Since \(1 < 3\), use \(k'(x) = -1\). So, \(k'(1) = -1\).- For \(x = 4\): Since \(4 \geq 3\), use \(k'(x) = 1\). So, \(k'(4) = 1\).- For \(x = 10\): Since \(10 \geq 3\), use \(k'(x) = 1\). So, \(k'(10) = 1\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Piecewise Functions
Piecewise functions are a fascinating part of calculus. They are defined by different expressions depending on the input value. These functions have multiple sub-functions, each with its own interval of validity. This is exactly what happens with the function \(k(x) = |x-3| + 2\), which can be rewritten into two separate linear functions based on the value of \(x\):
- If \(x \geq 3\), \(k(x)\) aligns with the line \(k(x) = x - 1\).
- If \(x < 3\), \(k(x)\) follows \(k(x) = 5 - x\).
Absolute Value Functions
Absolute value functions are unique because they transform all negative inputs to positive values. Graphically, these functions create a characteristic "V" shape with a vertex at the point where the expression inside the absolute value is zero. For \(k(x) = |x-3| + 2\), the absolute value \(|x-3|\) becomes zero at \(x=3\).
Absolute value functions are rewritten as piecewise functions to manage the operations within different intervals:
Absolute value functions are rewritten as piecewise functions to manage the operations within different intervals:
- If the expression inside is non-negative, such as \(x-3\) for \(x\geq 3\), the absolute value does not alter it.
- If the expression inside is negative, as in \(3-x\) for \(x < 3\), it negates the expression to ensure positivity.
Non-differentiability
Differentiability is an essential concept in calculus, indicating whether a function has a derivative at a given point. Some functions, like absolute value functions, are not differentiable everywhere.
For the function \(k(x) = |x-3| + 2\), non-differentiability happens at \(x=3\). Why? Because there's a sharp corner or cusp at this point due to the absolute value function. This corner prevents a tangent line from being drawn, resulting in the function lacking a derivative there.
Recognizing non-differentiability is vital for accurate derivative evaluation and understanding a function's behavior.
For the function \(k(x) = |x-3| + 2\), non-differentiability happens at \(x=3\). Why? Because there's a sharp corner or cusp at this point due to the absolute value function. This corner prevents a tangent line from being drawn, resulting in the function lacking a derivative there.
Recognizing non-differentiability is vital for accurate derivative evaluation and understanding a function's behavior.
Derivative Evaluation
Evaluating the derivatives of piecewise functions involves examining each segment separately. For the piecewise representation of our original function \(k(x)\):
- For \(x < 3\), the expression is \(5-x\) with a derivative \(k'(x) = -1\).
- For \(x \geq 3\), the expression is \(x-1\) with a derivative \(k'(x) = 1\).
- At \(x=0\) and \(x=1\), both less than 3, the derivative is \(-1\).
- At \(x=4\) and \(x=10\), both greater or equal to 3, the derivative is \(1\).