Chapter 6: Problem 328
For the following exercises, compute dy/dx by differentiating ln y. $$y=x^{-1 / \ln x}$$
Short Answer
Expert verified
The derivative \(\frac{dy}{dx} = 0\).
Step by step solution
01
Apply the Natural Logarithm
To solve for \(\frac{dy}{dx}\), start by applying the natural logarithm to both sides of the equation. Given \(y = x^{-1/\ln{x}}\), take the natural logarithm:\[\ln{y} = \ln{(x^{-1/\ln{x}})}\] This simplifies to:\[\ln{y} = -\frac{1}{\ln{x}} \cdot \ln{x} = -1\]
02
Differentiate Both Sides
Now, differentiate both sides of the equation with respect to \(x\). Differentiating the left side:\[\frac{d}{dx} (\ln{y}) = \frac{1}{y} \cdot \frac{dy}{dx}\]The derivative of the right side (which is a constant \(-1\)) with respect to \(x\):\[\frac{d}{dx}(-1) = 0\]Thus, we have:\[\frac{1}{y} \cdot \frac{dy}{dx} = 0\]
03
Solve for \(\frac{dy}{dx}\)
Solve the equation \(\frac{1}{y} \cdot \frac{dy}{dx} = 0\) for \(\frac{dy}{dx}\) by multiplying both sides by \(y\):\[\frac{dy}{dx} = y \cdot 0 = 0\]Hence, \(\frac{dy}{dx} = 0\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative of Logarithmic Functions
Derivatives are fundamental in calculus as they measure how a function changes as its input changes. For logarithmic functions, the key rule is essential. The derivative of the natural logarithm, \( \ln(x) \), is \( \frac{1}{x} \). Applying this rule helps in differentiating more complex expressions involving logs.
In the given exercise, we have a function in terms of \( y \) defined as \( y = x^{-1/\ln{x}} \). The first step to find \( \frac{dy}{dx} \) is to apply a logarithm on both sides. This allows us to simplify and facilitate the differentiation process:
In the given exercise, we have a function in terms of \( y \) defined as \( y = x^{-1/\ln{x}} \). The first step to find \( \frac{dy}{dx} \) is to apply a logarithm on both sides. This allows us to simplify and facilitate the differentiation process:
- Taking logarithms helps transform multiplicative and exponential expressions into more manageable additive forms.
- For differentiating the expression \( y = x^{-1/\ln{x}} \), finding the derivative of \( \ln(y) \) simplifies the process.
Natural Logarithm
The natural logarithm, denoted as \( \ln \), is the logarithm to the base \( e \), where \( e \approx 2.71828 \). It's an important function in calculus due to its unique properties:
The expression \( \ln{(x^{-1/\ln{x}})} = -\frac{1}{\ln{x}} \cdot \ln{x} \) ultimately simplifies to a constant \(-1\), making the differentiation straightforward.
- The derivative of \( \ln(x) \) is always \( \frac{1}{x} \), making it handy to simplify complex differentiation.
- It turns products into sums, which is particularly useful when dealing with exponents and roots.
- In our exercise, understanding \( \ln{x} \)'s behavior is crucial for simplifying the expression \( x^{-1/\ln{x}} \).
The expression \( \ln{(x^{-1/\ln{x}})} = -\frac{1}{\ln{x}} \cdot \ln{x} \) ultimately simplifies to a constant \(-1\), making the differentiation straightforward.
Solving Differential Equations
Solving differential equations involves finding an expression for the derivative \( \frac{dy}{dx} \). In the context of this exercise, we set up the equation \( \frac{1}{y} \cdot \frac{dy}{dx} = 0 \) after differentiating both sides.
To solve this:
Understanding how to manipulate the equation to reach this conclusion is a key part of solving differential equations, showcasing the synergy between algebraic manipulation and calculus principles.
To solve this:
- Since the right-hand side of the equation is zero, it implies that the entire left-hand side must equal zero.
- When solving \( \frac{1}{y} \cdot \frac{dy}{dx} = 0 \), we multiply through by \( y \), resulting in \( \frac{dy}{dx} = 0 \).
Understanding how to manipulate the equation to reach this conclusion is a key part of solving differential equations, showcasing the synergy between algebraic manipulation and calculus principles.