Chapter 6: Problem 21
Evaluate the given improper integral. \(\int_{0}^{\pi} \sec ^{2} x d x\)
Short Answer
Expert verified
The integral evaluates to 0.
Step by step solution
01
Understand the integral and identify substitutions
The given integral is \( \int_{0}^{\pi} \sec^2 x \, dx \). We need to evaluate this improper integral over the interval \([0, \pi]\). Remember that \( \sec^2 x \) is the derivative of \( \tan x \).
02
Set up the indefinite integral
Since the integral of \( \sec^2 x \) is \( \tan x \), we can write the antiderivative as \( \tan x + C \), where \( C \) is the constant of integration.
03
Evaluate the definite integral from 0 to \( \pi \)
Now, evaluate the definite integral using the Fundamental Theorem of Calculus: \[ \int_{0}^{\pi} \sec^2 x \, dx = \left[ \tan x \right]_{0}^{\pi} = \tan(\pi) - \tan(0). \]
04
Substitute the bounds into the antiderivative
Evaluate \( \tan(\pi) \) and \( \tan(0) \). We know that \( \tan(\pi) = 0 \) and \( \tan(0) = 0 \). Therefore, \[ \left[ \tan x \right]_{0}^{\pi} = 0 - 0 = 0. \]
05
Analyze for improper behavior
Although the function \( \sec^2 x \) is undefined at \( x = \frac{\pi}{2} \), the symmetry of the function and its antiderivative results in a cancellation, leading to a finite value of 0.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Antiderivative
In calculus, the concept of an antiderivative is about finding a function whose derivative gives us back our original function. In simpler terms, if we're given a derivative, the antiderivative is the function we started with before differentiating it. For our integral \( \int \sec^2 x \, dx \), secant squared \( (\sec^2 x) \) is the derivative of the tangent function \( (\tan x) \). This means that \( \tan x \) is the antiderivative of \( \sec^2 x \). Knowing this, it allows us to rewrite indefinite integrals in terms of known functions plus a constant \( C \), which is important because differentiation eliminates constants.
- The antiderivative of simple trigonometric functions is crucial for solving integrals involving them.
- It turns the process of integrating from one of raw computation into using known forms.
Definite Integral
A definite integral is an integral with specified limits of integration, such as \( a \) and \( b \). For our exercise, this is the interval from 0 to \( \pi \). Unlike indefinite integrals which have the constant \( C \), definite integrals provide a precise value representing the signed area under the curve. Evaluating the definite integral \( \int_{0}^{\pi} \sec^2 x \, dx \) involves finding the antiderivative \( \tan x \) at the bounds 0 and \( \pi \), then subtracting these values. To solve, we compute:
- \( \left[ \tan x \right]_{0}^{\pi} = \tan(\pi) - \tan(0) \)
- Both \( \tan(0) \) and \( \tan(\pi) \) are 0, giving us a final result of 0.
Fundamental Theorem of Calculus
The Fundamental Theorem of Calculus serves as a bridge between derivatives and integrals, showing how these concepts are interconnected. It can be divided into two main parts: the first part establishes that the process of differentiation can be reversed by integration, leading to the idea of the antiderivative. The second part shows that the definite integral of a function can be computed using its antiderivative. In solving our definite integral \( \int_{0}^{\pi} \sec^2 x \, dx \), this theorem is critical. It tells us that:
- We can find the integral's result by calculating the antiderivative at the bounds set by the limits (in our case, 0 and \( \pi \)).
- By computing \( \tan(\pi) - \tan(0) = 0 - 0 \), it confirms that even if the function seems undefined at a point within the interval, the structure of the integral can provide a finite, real result.