Problem 33 - Applied Calculus

Question

Find each indefinite integral. \(\int \frac{x e^{x}+1}{x} d x\)

Step-by-Step Solution

Answer

The indefinite integral is \( e^{x} + \ln|x| + C \).

Step 1: Simplify the expression

First, simplify the integrand by splitting the fraction: \( \int \left( \frac{x e^{x}}{x} + \frac{1}{x} \right) dx = \int (e^{x} + \frac{1}{x}) dx \). This allows us to integrate each part separately.

Step 2: Integrate each term

Now, integrate each term separately:- The integral of \( e^{x} \) is \( e^{x} \).- The integral of \( \frac{1}{x} \) is \( \ln|x| \) (natural logarithm of the absolute value of \( x \)).Thus, \[ \int (e^{x} + \frac{1}{x}) dx = e^{x} + \ln|x| + C, \] where \( C \) is a constant of integration.

Key Concepts

Integration by Parts

Integration by parts is a powerful technique often used when an integral is too complex for simple methods. This technique is based on the product rule for differentiation and helps in breaking down complex products into simpler parts. The formula for integration by parts is:\[\int u \, dv = uv - \int v \, du\]This means that if we have an integral that is a product of two functions, we can express it in parts. Here, \( u \) and \( dv \) are functions chosen from the integrand, and \( du \) and \( v \) are their respective derivatives and antiderivatives. To effectively use this method,

• Choose \( u \) to be a function that becomes simpler upon differentiation.
• Choose \( dv \) so its integration is straightforward.

In practice, remember the acronym LIATE (Logarithmic, Inverse trigonometric, Algebraic, Trigonometric, Exponential) to prioritize selecting \( u \). This approach is useful when integrating products involving polynomials, exponentials, logarithms, or trigonometric functions.

Natural Logarithm

The natural logarithm, represented by \( \ln(x) \), is the logarithm to the base \( e \), where \( e \) is an irrational constant approximately equal to 2.71828. It is the inverse function of the exponential function with base \( e \) and has properties that make it especially useful in calculus. Some key points about the natural logarithm include:

• \( \ln(e) = 1 \) since \( e^1 = e \).
• \( \ln(ab) = \ln(a) + \ln(b) \) for positive values of \( a \) and \( b \).
• \( \ln(1/x) = -\ln(x) \), meaning it's odd with respect to its argument.

In calculus, the derivative of \( \ln|x| \) is \( \frac{1}{x} \), and thus, the integral of \( \frac{1}{x} \) is \( \ln|x| + C \). Because of these properties, natural logarithms often simplify the integration and differentiation of functions where one of the divisors is a multiple of \( x \).

Exponential Function

The exponential function, traditionally written as \( e^x \), is a fundamental mathematical function that appears frequently in growth, decay, and differential equations. Its base, \( e \), is a transcendental number that naturally arises in processes involving continuous growth or decay. Here are some important aspects about the exponential function:

• The function is its own derivative, meaning that \( \frac{d}{dx}e^x = e^x \).
• It is also its own integral, implying \( \int e^x \, dx = e^x + C \).
• The function grows very fast; indeed, faster than any polynomial.

As a constant of natural importance, \( e \) serves as the base for the natural exponential function, which is prevalent in settings ranging from compound interest calculations to the solutions of differential equations. Thus, the simplicity of its differentiation and integration makes \( e^x \) a favorite in calculus, aiding engineers, physicists, and mathematicians in their work.