Chapter 4: Problem 38
Differentiate $$ g(N)=r N\left(1-\frac{N}{K}\right) $$ with respect to \(N\). Assume that \(K\) and \(r\) are positive constants.
Short Answer
Expert verified
The derivative is \( g'(N) = r - \frac{2rN}{K} \).
Step by step solution
01
Apply the Product Rule
The function \( g(N) = rN \left(1 - \frac{N}{K}\right) \) is a product of two functions: \( rN \) and \( 1 - \frac{N}{K} \). To differentiate this, we'll use the product rule, which states that \( (uv)' = u'v + uv' \), where \( u = rN \) and \( v = 1 - \frac{N}{K} \).
02
Differentiate the First Part of the Product
First, find the derivative of \( u = rN \) with respect to \( N \). The derivative \( u' \) is simply \( r \) because \( r \) is a constant and the derivative of \( N \) is 1.
03
Differentiate the Second Part of the Product
Next, differentiate \( v = 1 - \frac{N}{K} \) with respect to \( N \). The derivative \( v' \) is \( -\frac{1}{K} \) because the derivative of 1 is 0 and \( \frac{N}{K} \) differentiates to \( \frac{1}{K} \).
04
Apply the Product Rule Formula
Plug the differentiated parts into the product rule formula: \[ g'(N) = u'v + uv' = r\left(1 - \frac{N}{K}\right) + rN\left(-\frac{1}{K}\right) \] Simplify each term.
05
Simplify the Expression
Distribute and simplify the expression. The first term becomes: \[ r - \frac{rN}{K} \] The second term becomes: \[ -\frac{rN}{K} \] Combine the two terms to finalize: \[ g'(N) = r - \frac{2rN}{K} \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Product Rule
When faced with a function that is a product of two smaller functions, like in our exercise, the product rule is a very handy tool. The product rule states that if you have two functions, say \( u \) and \( v \), their product \( uv \) differentiates like this: \( (uv)' = u'v + uv' \). Here, \( u' \) and \( v' \) are the derivatives of \( u \) and \( v \) with respect to the variable you're considering. This rule allows us to handle complex expressions by breaking them into simpler parts.
If your expression is \( g(N) = rN \left(1 - \frac{N}{K}\right) \), it's composed of \( u = rN \) and \( v = 1 - \frac{N}{K} \). This means:
If your expression is \( g(N) = rN \left(1 - \frac{N}{K}\right) \), it's composed of \( u = rN \) and \( v = 1 - \frac{N}{K} \). This means:
- First, differentiate \( u \), which results in \( u' = r \).
- Then, differentiate \( v \), giving \( v' = -\frac{1}{K} \).
- Finally, plug these into the product rule formula to get the overall derivative.
Differentiation
Differentiation is a fundamental concept in calculus, crucial for understanding how a function changes with respect to a variable. It involves finding the derivative, which is essentially the rate of change of that function.
When you differentiate, you analyze how small changes in the input (or variable, like \( N \)) affect the output. The derivative answers the question: "How does the function value change as my variable changes slightly?"
In the context of our exercise, differentiation helps us understand how \( g(N) = rN \left(1 - \frac{N}{K}\right) \) changes as \( N \) changes.
When you differentiate, you analyze how small changes in the input (or variable, like \( N \)) affect the output. The derivative answers the question: "How does the function value change as my variable changes slightly?"
In the context of our exercise, differentiation helps us understand how \( g(N) = rN \left(1 - \frac{N}{K}\right) \) changes as \( N \) changes.
- For \( u = rN \), the derivative \( u' \) was simply \( r \), showing a constant change rate.
- For \( v = 1 - \frac{N}{K} \), the derivative \( v' \) was \(-\frac{1}{K} \), indicating a linear decrease.
- Combining using the product rule gives a complete picture of \( g'(N) \).
Calculus for Biology
In biology, calculus can help us model and understand complex systems. Biological systems often involve non-linear functions, much like population growth or decay models. Calculus provides tools such as differentiation to study these models.
For instance, in population dynamics, the function \( g(N) = rN \left(1 - \frac{N}{K}\right) \) might represent the rate of growth of a population, where \( N \) is the population size, \( r \) is the growth rate, and \( K \) is the carrying capacity. Here, calculus helps:
For instance, in population dynamics, the function \( g(N) = rN \left(1 - \frac{N}{K}\right) \) might represent the rate of growth of a population, where \( N \) is the population size, \( r \) is the growth rate, and \( K \) is the carrying capacity. Here, calculus helps:
- Differentiation allows us to find changes in population growth rates.
- Understanding these changes helps in managing or predicting population sizes more effectively.