Chapter 4: Problem 6
Evaluate the indicated integral. $$\int \sec ^{2} x \sqrt{\tan x} d x$$
Short Answer
Expert verified
\(\frac{2}{3} \tan ^{3/2} x + C\)
Step by step solution
01
Substitution
Let \(u = \tan x\). Then the differential \(du\) is \(du = \sec^2 x \, dx\). This substitution transforms the original integral into \(\int u^{1/2} \, du\).
02
Solve the New Integral
To solve \(\int u^{1/2} \, du\) is straightforward application of the power rule. The power rule states that the integral of \(x^n\) is \(\frac{1}{n+1}x^{n+1}\), so the integral becomes \(\frac{2}{3} u^{3/2}\).
03
Replace \(u\) with \(\tan x\)
Substitute \(u = \tan x\) back into the integral: \(\frac{2}{3} u^{3/2} = \frac{2}{3} \tan ^{3/2} x\).
04
Determine the Constant of Integration
Don't forget to determine the constant of integration after carrying out the integral. Thus, the final result is \(\frac{2}{3} \tan ^{3/2} x + C\), 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.
Integral Substitution
Integral substitution is a method used to simplify complex integrals. It often involves substituting part of the original integrand (the function being integrated) with a new variable. This transformation makes the integral easier to evaluate. In the given exercise, we use substitution by setting \(u = \tan x\). This choice helps because the derivative of \(\tan x\) is \(\sec^2 x\), which already appears in our integral.
- Finding \(du\): Once we define \(u\), we find the differential \(du = \sec^2 x \, dx\). This replacement directly matches part of our original integrand.
- Transforming the integral: The substitution changes the original integral \(\int \sec^2 x \sqrt{\tan x} \, dx\) to \(\int u^{1/2} \, du\).
Power Rule for Integration
The power rule is a fundamental principle in calculus for integrating functions of the form \(x^n\). According to this rule, the integral of \(x^n\) with respect to \(x\) can be found using \[ \int x^n \, dx = \frac{1}{n+1} x^{n+1} + C, \] where \(n eq -1\). This rule is easy to apply and particularly useful for polynomials and polynomial-like functions.
In our exercise, after substitution, the integral becomes \(\int u^{1/2} \, du\). We apply the power rule by setting \(n = \frac{1}{2}\). After integration, this results in \(\frac{2}{3} u^{3/2}\).
In our exercise, after substitution, the integral becomes \(\int u^{1/2} \, du\). We apply the power rule by setting \(n = \frac{1}{2}\). After integration, this results in \(\frac{2}{3} u^{3/2}\).
- Simplifying the expression: The rule transforms complex expressions to simpler forms, allowing us to solve integrals by handling powers of variables straightforwardly.
- Including the constant of integration: Remember that when calculating indefinite integrals, we add a constant \(C\). It accounts for any constant differences between antiderivatives.
Definite and Indefinite Integrals
Integrals can be classified as either definite or indefinite.
- Indefinite Integrals: These integrals lack specific boundaries and lead to a family of functions characterized by a constant of integration \(C\). They are represented as \(\int f(x) \, dx = F(x) + C\). In our solution, since no limits of integration are given, the result *\(\frac{2}{3} \tan^{3/2} x + C\)* represents an indefinite integral.
- Definite Integrals: These are calculated over a specific interval \([a, b]\) and yield a numerical result \(\int_{a}^{b} f(x) \, dx\), describing the area under the curve \(f(x)\) from \(x = a\) to \(x = b\). Although not directly required here, it's important to understand how they contrast from indefinite integrals.