Chapter 5: Problem 24
Evaluate the integrals using Part 1 of the Fundamental Theorem of Calculus. $$ \int_{1 / 2}^{1} \frac{1}{2 x} d x $$
Short Answer
Expert verified
The integral evaluates to \( \frac{1}{2} \ln(2) \).
Step by step solution
01
Identify the Function and Interval
The integral we need to solve is \( \int_{1 / 2}^{1} \frac{1}{2x} \, dx \). This means we need to integrate the function \( f(x) = \frac{1}{2x} \) over the interval \([\frac{1}{2}, 1]\).
02
Find the Antiderivative
To solve the integral, we need to find the antiderivative of \( \frac{1}{2x} \). Notice that \( \frac{1}{2x} \) can be written as \( \frac{1}{2} \cdot \frac{1}{x} \), which simplifies the process. The antiderivative of \( \frac{1}{x} \) is \( \ln|x| \). So, the antiderivative is \( \frac{1}{2} \ln|x| \).
03
Apply the Fundamental Theorem of Calculus
According to Part 1 of the Fundamental Theorem of Calculus, the value of the definite integral \( \int_{a}^{b} f(x) \, dx \) is given by \( F(b) - F(a) \), where \( F(x) \) is the antiderivative of \( f(x) \). Here, \( F(x) = \frac{1}{2} \ln|x| \).
04
Evaluate the Antiderivative at the Bounds
Substitute the bounds into the antiderivative:1. \( F(1) = \frac{1}{2} \ln|1| = \frac{1}{2} \cdot 0 = 0 \).2. \( F\left( \frac{1}{2} \right) = \frac{1}{2} \ln\left| \frac{1}{2} \right| = \frac{1}{2} \ln\left( \frac{1}{2} \right) \).
05
Calculate the Definite Integral
Now, compute the definite integral: \[ \int_{1/2}^{1} \frac{1}{2x} \, dx = F(1) - F\left( \frac{1}{2} \right) = 0 - \left( \frac{1}{2} \ln\left( \frac{1}{2} \right) \right) \]This simplifies further to:\[ -\frac{1}{2} \ln\left( \frac{1}{2} \right) \]This can also be written as:\[ \frac{1}{2} \ln(2) \] because \( \ln\left( \frac{1}{2} \right) = - \ln(2) \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Definite Integral
A definite integral is a calculation that produces a single number, representing the accumulation of quantities over a specified interval. Think of it like adding up small slices to find a total.
- Purpose: It helps us find areas under curves, total distances, or even quantities like mass when density is variable over a range.
- Notation: The definite integral of a function \( f(x) \) from \( a \) to \( b \) is denoted as \( \int_{a}^{b} f(x) \, dx \).
- Result: The output is just a number, representing the total accumulation from point \( a \) to point \( b \).
Antiderivative
An antiderivative is like the opposite of a derivative. While derivatives measure how a function changes, antiderivatives help us "reverse" this process.
- Finding: To find an antiderivative, you look for a function whose derivative gives you the original function you're interested in.
- Example: In our case, we needed the antiderivative of \( \frac{1}{2x} \). This function can be rewritten as \( \frac{1}{2} \cdot \frac{1}{x} \), leading us to recognize it as a logarithmic function.
- Application: The antiderivative is key to evaluating definite integrals, which is why knowing \( \frac{1}{2}\ln|x| \) was crucial in solving our exercise.
Logarithmic Function
Logarithmic functions are intimately tied to the process of integration, especially when dealing with reciprocals or fractions.
- Definition: A logarithmic function with base \( e \) (Euler's number, approximately 2.718) is usually expressed as \( \ln(x) \), called the natural logarithm.
- Properties: This function has unique properties that make it useful for integration, such as \( \ln(1) = 0 \) and \( \ln(ab) = \ln(a) + \ln(b) \).
- Relevance: In our exercise, \( \frac{1}{x} \) was the function from which the logarithmic antiderivative was derived. Recognizing this connection simplifies the process of integration.