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Find each indefinite integral. \(\int-5 x^{-1} d x\)

Short Answer

Expert verified
The integral is \(-5\ln|x| + C\).

Step by step solution

01

Identify the Integral Formula

The given problem is to solve \(\int -5x^{-1} \, dx\). This is an indefinite integral, and we will use the formula \(\int x^n \, dx = \frac{x^{n+1}}{n+1} + C\) for \(n eq -1\). However, since \(n = -1\), the integral becomes a special case that involves the natural logarithm.
02

Apply the Special Formula for \(x^{-1}\)

When \(n = -1\), the rule \(\int x^{-1} \, dx = \ln|x| + C\) applies. In this problem, we have \(-5x^{-1}\), so we factor out the constant multiplier and rewrite the integral as \(-5 \int x^{-1} \, dx\).
03

Integrate the Function

Using the formula, we integrate: \(-5 \int x^{-1} \, dx = -5 \ln|x| + C\). The constant \(-5\) is multiplied with the result of the integral of \(x^{-1}\), which is \(\ln|x|\).
04

Write the Final Result

The indefinite integral \(\int -5x^{-1} \, dx\) is \(-5\ln|x| + C\), where \(C\) is the constant of integration.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Logarithmic Integration
Logarithmic integration is a technique used when dealing with the integration of functions involving the reciprocal of a variable, typically in the form of \(x^{-1}\). This situation is unique because the standard power rule does not apply when \(n = -1\). Instead, the integral of \(x^{-1}\) leads to a natural logarithm, specifically: \[ \int x^{-1} \, dx = \ln|x| + C \] where \(C\) is the constant of integration. This formula is crucial because it accounts for the nature of the function being undefined at zero, hence why the absolute value is used in the logarithm to ensure the function remains within the realm of real numbers. This concept is particularly helpful when dealing with integrals of functions that mimic the behavior of \(x^{-1}\). By focusing on logarithmic integration, one can tackle problems involving reciprocal functions more effectively.
Integration Techniques
Understanding various integration techniques is essential for solving calculus problems. The power of these techniques lies in their ability to simplify complex integrals into calculable forms. Here's a simple breakdown of when different techniques might be used:
  • Basic Power Rule: Used for integrals of the form \(x^n\) where \(n eq -1\).
  • Logarithmic Rule: As discussed, employed when \(n = -1\) to yield natural logarithms.
  • Substitution: Useful for integrals that can be turned into a simpler form by substituting variables.
  • Integration by Parts: Specially used when dealing with products of functions where substitution isn't straightforward.
In the example provided, the use of a logarithmic rule showed how extracting the constant (-5) from the original integral allowed us to directly apply the known formula for \(x^{-1}\), resulting in a simplified and elegant solution.
Calculus Problem Solving
Solving calculus problems often requires a strategic approach, integrating various methods as part of a bigger problem-solving toolkit. Here’s how you can enhance your calculus problem-solving skills:
  • Identify Key Characteristics: Begin by identifying the type of function you are dealing with. Look for traits such as powers of \(x\), exponential, trigonometric, or reciprocal forms.
  • Choose Appropriate Techniques: Based on the function type, choose the most suitable technique. For \(x^{-1}\) integrals, go for logarithmic integration.
  • Check Your Work: After finding an integral, differentiate it to verify. For example, differentiating \(-5\ln|x| + C\) should give you back \(-5x^{-1}\).
By consistently practicing these strategies across different types of integrals, you build confidence and proficiency in calculus problem solving. Remember, every problem is an opportunity to apply your understanding of integration techniques.

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Most popular questions from this chapter

BUSINESS: Capital Value of an Asset The capital value of an asset (such as an oil well) that produces a continuous stream of income is the sum of the present value of all future earnings from the asset. Therefore, the capital value of an asset that produces income at the rate of \(r(t)\) dollars per year (at a continuous interest rate \(i\) ) is $$ \left(\begin{array}{c} \text { Capital } \\ \text { value } \end{array}\right)=\int_{0}^{T} r(t) e^{-i t} d t $$ where \(T\) is the expected life (in years) of the asset. Use the formula in the preceding instructions to find the capital value (at interest rate \(i=0.05)\) of a uranium mine that produces income at the rate of \(r(t)=560,000 t^{1 / 2}\) dollars per year for 20 years.

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