Chapter 7: Problem 22
Evaluate the integrals. $$\int e^{\csc (\pi+t)} \csc (\pi+t) \cot (\pi+t) d t$$
Short Answer
Expert verified
The integral evaluates to \(-e^{\csc(\pi+t)} + C\).
Step by step solution
01
Identify Substitution Component
Notice that the integral involves an exponential function with a trigonometric argument. Typically, for integrals of the form \( e^u u' \, dt \), we use substitution. Here, we have \( u = \csc(\pi + t) \), whose derivative is \( -\csc(\pi + t) \cot(\pi + t) \). This matches part of the integral.
02
Perform Substitution
Set \( u = \csc(\pi + t) \) and find \( du = -\csc(\pi + t) \cot(\pi + t) \, dt \). Notice that \( du = -d(t) \textb{ as } \csc(\pi + t) \cot(\pi + t) \, dt = -du \). To adapt the integral, multiply through by \(-1\), transforming our integral to \(-\int e^u \, du\).
03
Integrate the Expression
Now, integrate \(-\int e^u \, du\), which is a standard result: \(-e^u + C\). This is because the integral of \(e^u\) is \(e^u\), with the \(-1\) multiplicative constant included from the substitution adjustment.
04
Back-Substitute to Original Variable
Replace \(u\) with the original substitution: \(u = \csc(\pi + t)\). Hence, the integral becomes \(-e^{\csc(\pi + t)} + C\). This back-substitution returns the solution to the variable in the original integral.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Trigonometric Substitution
Trigonometric substitution is a technique used in calculus to simplify integrals by transforming complex trigonometric expressions into simpler algebraic forms. In this approach, we replace a trigonometric function with a variable, easing the integration process. In the given problem, we notice the presence of a trigonometric component, specifically, the cosecant
- First, identify a trigonometric function in the problem that complicates direct integration. Here, it's \( \csc(\pi + t) \).
- Then, set this function equal to a new variable, typically denoted as \(" u "\). For this exercise, \{ u = \csc(\pi + t) \}.
- Find the derivative of this new variable in terms of the original variable. This means calculating \{ du = -\csc(\pi + t) \cot(\pi + t) \, dt \}.
Exponential Functions
Exponential functions appear frequently in calculus, representing rapidly increasing or decreasing curves. They have the form
- The exponent can be any expression, which in this problem is \( e^{\csc(\pi+t)} \).
- Recognize exponential expressions of the form \( e^u \). These are immediately integrable to \( e^u \), up to a constant adjustment.
- After substituting \( u = \csc(\pi + t) \), the integral simplifies to \(- \int e^u \, du\).
Indefinite Integral
An indefinite integral is essentially the opposite of differentiation, representing a family of functions that alleviate the derivative back to an original function plus a constant. The symbol
- It encompasses all possible functions that could result in the original function's derivative, noted by the constant \( C \).
- For an expression like \( \int e^{\csc(\pi+t)} \csc(\pi+t) \cot(\pi+t) \, dt \), it involves reversing the differentiation process in a structured manner.
- After acknowledging the original substitution, integrate the transformed expression, where \( \int e^u \, du \) resolves to \( e^u + C \), and multiply by any constants derived from previous steps, notably the \(-1\) from \(-du\).