Chapter 6: Problem 27
Find the value of \(k\) that makes the antidifferentiation formula true. [Note: You can check your answer without looking in the answer section. How?] $$\int 2 e^{4 x-1} d x=k e^{4 x-1}+C$$
Short Answer
Expert verified
k = \frac{1}{2}\.
Step by step solution
01
Identify the function to be integrated
The given integral is \(\int 2 e^{4 x-1} d x\).
02
Use substitution method
Let \(u = 4x - 1\). Then, \(du = 4dx\), or \(dx = \frac{1}{4} du\).
03
Substitute in the integral
Substitute \(u = 4x - 1\) and \(dx = \frac{1}{4} du\) into the integral: \(\int 2 e^{4 x-1} d x = \int 2 e^{u} \frac{1}{4} du\).
04
Simplify the integral
Factor out the constants from the integral: \(\int 2 e^{4 x - 1} d x = \frac{1}{2} \int e^{u} du\).
05
Integrate with respect to u
Since the integral of \(e^{u}\) with respect to \(u\) is \(e^{u}\), we have \(\frac{1}{2} e^{u} + C\).
06
Substitute back the value of u
Replace \(u\) with \(4x - 1\) to get the antiderivative in terms of x. Therefore, \(\frac{1}{2} e^{4 x - 1} + C\).
07
Determine the value of k
Compare this result with the given form \(\text{k}\text{ }e^{4 x-1}+C\). We see that \(\text{k} = \frac{1}{2}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Integration by Substitution
Integration by substitution is a method used to simplify complex integrals. This method involves substituting a part of the integral with a new variable to make the integral easier to solve. To understand this, let's look at a basic idea: change of variable.
In our example, we started with the integral \(\int 2 e^{4 x-1} \, dx\).
Here are the steps we followed:
In our example, we started with the integral \(\int 2 e^{4 x-1} \, dx\).
Here are the steps we followed:
- First, we identified a substitution that could simplify the integral. We let \(\text{ }u = 4 x - 1\). This means the integral becomes in terms of \(u\).
- We also need to change the differential \(dx\) to \(du\). By differentiating \(u\) with respect to \(x\), we get \, \(du = 4 dx\) or \(dx = \frac{1}{4} \, du\).
- We then substituted \(u\) and \(dx\) in the integral:\(\int 2 e^{4 x-1} \, dx = \int 2 e^{u} \frac{1}{4} \, du\).
- The next step was to simplify the integral by factoring out the constants, which gave us: \({\frac{1}{2}} \int e^{u} \, du\).
Exponential Functions
Exponential functions are functions that have constants raised to variable powers. They have the general form \(f(x) = a^x\), where \(a\) is a constant. A special case is when \(a = e\), where \(e\) is the base of the natural logarithm, approximately equal to 2.71828.
When integrating exponential functions like \(e^{u}\), the integral is straightforward:
When integrating exponential functions like \(e^{u}\), the integral is straightforward:
- For \(\int e^u \, du\), the result is simply \( e^u + C\). This is because the derivative of \(e^u\) is \(e^u\).
- Hence, when we integrated \({\frac{1}{2}} \int e^{u} \, du\), we got \({\frac{1}{2} e^u + C}\).
- Finally, we substituted back \(u = 4x - 1\) to return to our original variable, giving us \({\frac{1}{2} e^{4 x - 1} + C}\).
Definite Integrals
While our problem focused on an indefinite integral (which includes a constant of integration \(C\)), it's important to understand definite integrals too.
Definite integrals are those that have upper and lower bounds. They represent the area under the curve for a specific interval. For example:
\(\text{ }\int_{a}^{b} f(x) \, dx\) means finding the integral of \(f(x)\) from \(a\) to \(b\).
Definite integrals are those that have upper and lower bounds. They represent the area under the curve for a specific interval. For example:
\(\text{ }\int_{a}^{b} f(x) \, dx\) means finding the integral of \(f(x)\) from \(a\) to \(b\).
- To compute a definite integral, we first find the indefinite integral (antiderivative) of \(f(x)\).
- Then, we evaluate this antiderivative at the upper limit \(b\) and subtract its value at the lower limit \(a\).
- This process provides the net area under the curve between \(x = a\) and \(x = b\).