Chapter 6: Problem 34
Find the value of \(k\) that makes the antidifferentiation formula true. [Note: You can check your answer without looking in the answer section. How?] $$\int(2 x-1)^{3} d x=k(2 x-1)^{4}+C$$
Short Answer
Expert verified
The value of k is \( \frac{1}{8} \).
Step by step solution
01
- Recognize the Given Indefinite Integral
The given indefinite integral is \( \int (2x-1)^3 \, dx \). The goal is to find the value of \( k \) that makes the antidifferentiation formula true.
02
- Perform a Substitution
Let \( u = 2x - 1 \). Therefore, \( du = 2 \, dx \), or \( dx = \frac{du}{2} \). The integral becomes: \[ \int (2x-1)^3 \, dx = \int u^3 \cdot \frac{1}{2} \, du = \frac{1}{2} \int u^3 \, du \]
03
- Apply the Power Rule for Integration
The power rule states that \( \int u^n \, du = \frac{u^{n+1}}{n+1} + C \). Applying this rule to our integral: \[ \frac{1}{2} \int u^3 \, du = \frac{1}{2} \left( \frac{u^{4}}{4} \right) + C = \frac{1}{8} u^4 + C \]
04
- Substitute Back the Original Variable
Recall that \( u = 2x - 1 \). Substitute \( u \) back into the expression: \[ \frac{1}{8} (2x - 1)^4 + C \]
05
- Identify \( k \)
Compare the resulting expression \( \frac{1}{8} (2x - 1)^4 + C \) with the form \( k(2x - 1)^4 + C \). It is evident that \( k = \frac{1}{8} \).
06
- Verify the Solution
Differentiate \( k(2x - 1)^4 + C \) to ensure it matches the original integrand: \[ \frac{d}{dx} \left( \frac{1}{8} (2x - 1)^4 + C \right) = \frac{1}{8} \cdot 4(2x - 1)^3 \cdot 2 = (2x - 1)^3 \]. This matches the original integrand.
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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 type of integral that calculates the net area under a curve within specified limits, usually between points \(a\) and \(b\).
Unlike an indefinite integral, which represents a family of functions and includes a constant \(C\), a definite integral gives a numerical value.
The notation for a definite integral is \[ \int_a^b f(x) \, dx. \]
Here’s a simple way to understand it:
Unlike an indefinite integral, which represents a family of functions and includes a constant \(C\), a definite integral gives a numerical value.
The notation for a definite integral is \[ \int_a^b f(x) \, dx. \]
Here’s a simple way to understand it:
- Take the definite integral of a function to find the accumulated quantity over an interval.
- For example, if the function represents velocity over time, the definite integral gives the total distance traveled.
- The computation involves finding the antiderivative (indefinite integral) first and then evaluating this antiderivative at the boundary points \(a\) and \(b\).
substitution method
The substitution method is a powerful tool in integration, especially for handling more complex integrals. It simplifies an integral by changing variables.
Here's how it works:
Set \( u = 2x - 1 \). Thus, \( du = 2 \, dx \) or \( dx = \frac{du}{2} \). The integral changes to: \[ \int u^3 \cdot \frac{1}{2} \, du = \frac{1}{2} \int u^3 \, du. \]
This replacement makes the integral much more straightforward to compute.
Here's how it works:
- Identify a part of the integrand that can be set as a new variable, say \(u\).
- Replace the chosen part with \(u\) and determine \(du\) (the differential of \(u\)).
- Substitute both \(u\) and \(du\) into the integral, transforming it into an easier problem.
- Integrate with respect to \(u\).
- Finally, substitute back the original variable.
Set \( u = 2x - 1 \). Thus, \( du = 2 \, dx \) or \( dx = \frac{du}{2} \). The integral changes to: \[ \int u^3 \cdot \frac{1}{2} \, du = \frac{1}{2} \int u^3 \, du. \]
This replacement makes the integral much more straightforward to compute.
power rule for integrals
The power rule for integrals helps in integrating functions of the form \( u^n \).
The rule states: \[ \int u^n \, du = \frac{u^{n+1}}{n+1} + C, \] where \( n \) is any real number except \( -1 \).
Let's break it down:
Using the power rule, integrate \( u^3 \) as follows: \[ \frac{1}{2} \cdot \frac{u^4}{4} + C = \frac{1}{8} u^4 + C. \] This shows just how handy the power rule is.
Integral calculus becomes much more manageable with these key rules!
The rule states: \[ \int u^n \, du = \frac{u^{n+1}}{n+1} + C, \] where \( n \) is any real number except \( -1 \).
Let's break it down:
- It applies when the integrand is a power of the variable, making the integration process direct.
- Increment the exponent by 1 to get \( n+1 \).
- Divide by this new exponent.
- Don’t forget to add the constant of integration \( C \).
Using the power rule, integrate \( u^3 \) as follows: \[ \frac{1}{2} \cdot \frac{u^4}{4} + C = \frac{1}{8} u^4 + C. \] This shows just how handy the power rule is.
Integral calculus becomes much more manageable with these key rules!