Chapter 3: Problem 44
If \(g(x)=x / e^{x}, \text { find } g^{(n)}(x)\)
Short Answer
Expert verified
\( g^{(n)}(x) = \frac{n-x}{e^x} \) for any integer \( n \).
Step by step solution
01
Understand the Function
The function provided is \( g(x) = \frac{x}{e^x} \). This means we need to calculate the derivatives of this function multiple times to find a pattern for \( g^{(n)}(x) \).
02
Calculate the First Derivative
To find \( g'(x) \), we use the quotient rule, which is \( \left(\frac{u}{v}\right)' = \frac{u'v - uv'}{v^2} \). Here, \( u = x \) and \( v = e^x \). Thus, \( u' = 1 \) and \( v' = e^x \). The first derivative is:\[g'(x) = \frac{1 \cdot e^x - x \cdot e^x}{(e^x)^2} = \frac{e^x - xe^x}{e^{2x}} = \frac{e^x(1 - x)}{e^{2x}} = \frac{1 - x}{e^x}\]
03
Calculate the Second Derivative
Apply the quotient rule again to \( g'(x) = \frac{1-x}{e^x} \) with \( u = 1-x \) and \( v = e^x \). Thus, \( u' = -1 \) and \( v' = e^x \). The second derivative is:\[g''(x) = \frac{-1 \cdot e^x - (1-x)\cdot e^x}{(e^x)^2} = \frac{-e^x - e^x + xe^x}{e^{2x}} = \frac{x-2}{e^x}\]
04
Calculate the Third Derivative
Apply the quotient rule again to \( g''(x) = \frac{x-2}{e^x} \) with \( u = x-2 \) and \( v = e^x \). Thus, \( u' = 1 \) and \( v' = e^x \). The third derivative is:\[g'''(x) = \frac{1 \cdot e^x - (x-2)\cdot e^x}{(e^x)^2} = \frac{e^x - xe^x + 2e^x}{e^{2x}} = \frac{3-x}{e^x}\]
05
Identify and Confirm the Pattern
The pattern appears to be \( g^{(n)}(x) = \frac{n-x}{e^x} \). To confirm, it is helpful to derive \( g^{(4)}(x) \) using the same method:\[g^{(4)}(x) = \frac{4-x}{e^x}\]Thus, \( g^{(n)}(x) \) consistently fits this pattern for successive derivatives.
06
General Solution
The nth derivative of the function \( g(x) \) is \( g^{(n)}(x) = \frac{n-x}{e^x} \). This pattern matches for derivatives of all successive orders and confirms the relationship observed.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quotient Rule
The quotient rule is a fundamental tool in calculus, especially when dealing with functions expressed as the division of two sub-functions. When you have a function in the form \( g(x) = \frac{u}{v} \), where both \( u \) and \( v \) are differentiable functions of \( x \), you apply the quotient rule to find its derivative. The rule states:
- First, differentiate the numerator, \( u' \).
- Then, differentiate the denominator, \( v' \).
- The quotient rule formula is: \( \left( \frac{u}{v} \right)' = \frac{u'v - uv'}{v^2} \).
Pattern Recognition in Derivatives
Identifying patterns in derivatives is an invaluable skill, particularly when dealing with higher-order derivatives. After computing the first few derivatives, you may start noticing a regular structure or behavior in the outcomes. This occurs because of consistent applications of differentiation rules, like the quotient rule.
- Start with identifying the base function and its derivatives.
- Look for repeating components or constants in the derivative expressions.
- In our function, we noticed the recurring representation \( g^{(n)}(x) = \frac{n-x}{e^x} \).
Calculus for Life Sciences
In life sciences, calculus is used to model and analyze biological systems, involving rates of change and accumulation. Functions like \( g(x) = \frac{x}{e^x} \) might describe biological phenomena such as growth rates or decay processes. The capability to differentiate such functions helps us to understand key behaviors and progressions over time.
- Understand how quantities change in time or space.
- Predict the impact of changes in biological systems.
- Apply calculus to areas like population dynamics or pharmacokinetics.
Function Differentiation
Function differentiation is at the core of calculus, allowing us to understand how a function behaves as its input changes. To differentiate a function means to determine its rate of change, providing insights into its slope and curvature.
- Begin with simple functions and progress to more complex forms.
- Utilize rules like the quotient, product, and chain to find derivatives efficiently.
- Evaluate the behavior of the function across its domain through derivatives.