Problem 40 - Calculus Early Transcendentals: Pearson New International Edition

Question

Perform the indicated integrations. $$ \int \cosh 3 x d x $$

Step-by-Step Solution

Answer

\( \int \cosh(3x) \, dx = \frac{1}{3} \sinh(3x) + C \).

Step 1: Identify the Integral Form

The given problem is to integrate \( \int \cosh(3x) \, dx \). This is a standard integral that can be solved using a direct integration rule.

Step 2: Recall the Hyperbolic Integrals Rule

Recall that the integral of \( \cosh(ax) \) is \( \frac{1}{a}\sinh(ax) + C \), where \( C \) is the constant of integration. Here, \( a = 3 \).

Step 3: Apply the Hyperbolic Integrals Rule

Using the rule, the integral becomes \( \frac{1}{3} \sinh(3x) + C \). We apply the formula directly to find the integral.

Key Concepts

Hyperbolic Functions

Hyperbolic functions, much like their trigonometric counterparts, are essential in various aspects of calculus and engineering. They are defined using the exponential function and provide alternatives to trigonometric functions. The hyperbolic cosine function, denoted as \( \cosh(x) \), is defined as:

• \( \cosh(x) = \frac{e^x + e^{-x}}{2} \)

Another hyperbolic function that frequently appears in calculus is the hyperbolic sine, \( \sinh(x) \), defined by:

• \( \sinh(x) = \frac{e^x - e^{-x}}{2} \)

These functions have similar properties and rules as the trigonometric sine and cosine functions. For example, their derivatives are related such that the derivative of \( \cosh(x) \) is \( \sinh(x) \). This is helpful in performing symbolic mathematics, particularly integration, where these functions often replace trigonometric equations in more complex scenarios.

Integration Techniques

Integration is a fundamental technique in calculus used to find areas under curves and solve differential equations. In the case of hyperbolic functions, specific rules apply that simplify the integration process. When integrating hyperbolic functions such as \( \int \cosh(ax) \, dx \), knowing the formulas is vital.To integrate \( \cosh(ax) \), the rule is straightforward:

• The integral of \( \cosh(ax) \) is \( \frac{1}{a} \sinh(ax) + C \)

This formula comes directly from the properties of hyperbolic functions and is analogous to their trigonometric counterparts. Applying these known formulas can make finding antiderivatives much easier and is an efficient technique, particularly in definite and indefinite integration.

Definite and Indefinite Integrals

The integration process leads to two types of results: definite and indefinite integrals. Understanding the difference between these two is key in calculus.

• Indefinite integrals, such as \( \int \cosh(3x) \, dx \), include a constant \( C \), representing an entire family of functions. The result is \( \frac{1}{3} \sinh(3x) + C \).
• Definite integrals, on the other hand, evaluate the integral over a specific interval \([a, b]\) and yield a numerical value. For example, to find \( \int_{a}^{b} \cosh(3x) \, dx \), apply the fundamental theorem of calculus by substituting the interval into the result from the indefinite integration and calculate the difference.

Using either type of integration requires a solid understanding of the function you are working with and the correct application of known formulas. Building a strong foundation in these concepts is crucial for solving more complex calculus problems in mathematics and applied sciences.