Chapter 4: Problem 14
Evaluate using integration by parts or substitution. (Assume \(u>0\) in \(\ln\) u. Check by differentiating. $$ \int \ln (x+4) d x $$
Short Answer
Expert verified
\( \int \ln(x+4) \, dx = x \ln(x+4) - x + 4 \ln|x+4| + C \).
Step by step solution
01
Choose Substitution Variables
Choose to use integration by parts to solve the integral \( \int \ln(x+4) \, dx \). Using the formula for integration by parts, let \( u = \ln(x+4) \) and \( dv = dx \).
02
Compute Derivatives and Integrals
Differentiate \( u \) and integrate \( dv \). Set \( du = \frac{1}{x+4} \, dx \) and \( v = x \).
03
Apply Integration by Parts Formula
Substitute into the integration by parts formula \( \int u \, dv = uv - \int v \, du \). This gives us \( \int \ln(x+4) \, dx = x \ln(x+4) - \int x \frac{1}{x+4} \, dx \).
04
Simplify and Solve the Remaining Integral
Simplify \( \int x \frac{1}{x+4} \, dx \) to \( \int \left(1 - \frac{4}{x+4}\right) \, dx \) by dividing \( x \) by \( x+4 \). Thus, solve it as \( \int \, dx - \int \frac{4}{x+4} \, dx \).
05
Evaluate the Simplified Integral
Evaluate \( \int \, dx = x \) and \( \int \frac{4}{x+4} \, dx = 4 \ln|x+4| \). Thus, the entire answer is \( x \ln(x+4) - x + 4 \ln|x+4| + C \).
06
Check by Differentiating
Differentiate the result \( x \ln(x+4) - x + 4 \ln|x+4| + C \). Use the product rule and chain rule to confirm that the derivative simplifies back to \( \ln(x+4) \), which verifies the solution is correct.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Substitution Method
The substitution method is a helpful technique in calculus that simplifies integration problems. When you have an integral that seems tough to solve directly, substitution comes to the rescue by introducing a new variable. This can make complex expressions more manageable.
- Start by identifying a part of the integrand that can be substituted with a simpler variable.
- It's important to choose a substitution that simplifies the integral enough to make it solvable.
- After choosing a substitution, change all instances of the old variable in the original integral to the new variable to complete the substitution.
Calculus
Calculus is a branch of mathematics focused on limits, functions, derivatives, integrals, and infinite series. It's a powerful tool for analyzing changes and motion, foundational to many scientific disciplines.
- Differentiation focuses on derivate functions, emphasizing how things change.
- Integration, on the other hand, deals with summing over intervals and is crucial for finding areas under curves.
- These processes are used to solve real-world problems involving motion, growth, and forces.
Definite Integral
Definite integrals represent the accumulated value over an interval, essentially giving the area under a curve between two points. They are more than just an extension of indefinite integrals, offering precise calculations with limits.
- To solve a definite integral, determine the antiderivative first.
- Next, evaluate it at the upper and lower bounds of the given interval.
- Subtract the lower bound value from the upper bound value to get the final result.