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Evaluate the integrals using integration by parts. $$\int t^{2} e^{4 t} d t$$

Short Answer

Expert verified
\( \int t^2 e^{4t} dt = \frac{1}{4} t^2 e^{4t} - \frac{1}{8} t e^{4t} + \frac{1}{32} e^{4t} + C \)

Step by step solution

01

Identify Functions for Integration by Parts

For integration by parts, we need to identify two functions within the integrand: one to differentiate and one to integrate. Let's choose the algebraic function for differentiation and the exponential function for integration. Thus, let:\( u = t^2 \) and \( dv = e^{4t} dt \).
02

Differentiate and Integrate the Chosen Functions

Differentiate \( u \) and integrate \( dv \) to find \( du \) and \( v \):\( du = 2t \, dt \) \( v = \int e^{4t} \, dt = \frac{1}{4}e^{4t} \).
03

Apply the Integration by Parts Formula

The integration by parts formula is \( \int u \, dv = uv - \int v \, du \). Substitute the expressions found in the previous step:\( \int t^2 e^{4t} \, dt = t^2 \cdot \frac{1}{4}e^{4t} - \int \frac{1}{4}e^{4t} \cdot 2t \, dt \).
04

Simplify the Expression

Simplify the expression obtained in the previous step:\( \int t^2 e^{4t} \, dt = \frac{1}{4}t^2e^{4t} - \frac{1}{2}\int t e^{4t} \, dt \).
05

Apply Integration by Parts Again

We need to apply integration by parts again to solve \( \int t e^{4t} \, dt \). This time choose:\( u_1 = t \) and \( dv_1 = e^{4t} \, dt \).Thus, \( du_1 = 1 \, dt \) and \( v_1 = \frac{1}{4}e^{4t} \).
06

Use the Formula a Second Time

Apply the integration by parts formula again:\( \int t e^{4t} \, dt = \frac{1}{4}t e^{4t} - \int \frac{1}{4} e^{4t} \, dt \).
07

Evaluate the Remaining Integral

Evaluate the remaining integral:\( \int \frac{1}{4} e^{4t} \, dt = \frac{1}{16} e^{4t} + C \), where \( C \) is the constant of integration.
08

Combine Results for Complete Solution

Substitute back into the equation from Step 4:\( \int t^2 e^{4t} \, dt = \frac{1}{4}t^2e^{4t} - \frac{1}{2}\left( \frac{1}{4}t e^{4t} - \frac{1}{16} e^{4t} \right) \).
09

Simplify the Complete Expression

Expand and simplify the terms:\( \int t^2 e^{4t} \, dt = \frac{1}{4}t^2 e^{4t} - \frac{1}{8}t e^{4t} + \frac{1}{32}e^{4t} + C \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Integral Calculus
Integral calculus is all about accumulation of quantities. In simple terms, it deals with the concept of adding up infinitely small quantities to find totals. One of the fundamental tools used in integral calculus is integration, which is the process of finding the integral of a function. While there are several techniques to compute integrals, integration by parts is a method particularly useful when dealing with products of functions.Integration by parts follows from the product rule of differentiation and allows us to integrate complex expressions by transforming them into simpler forms. The essence of this method is encapsulated in the formula:\[\int u \, dv = uv - \int v \, du\]where \(u\) and \(dv\) are parts of the original integral, and \(du\) and \(v\) are their respective derivatives and integrals. This technique is often applied in sequences, as seen in the exercise, to break down difficult integrals into manageable steps.
Exponential Functions
Exponential functions are a class of functions where a constant base is raised to a variable exponent, such as \(e^{x}\). The function \(e^{x}\) is particularly special in calculus due to its unique properties.- **Self-Derivative**: The derivative of \(e^{x}\) is \(e^{x}\) itself, making it extremely straightforward when performing differentiation and integration.- **Growth Rate**: Exponential functions model growth rates that increase rapidly, making them useful in various fields such as biology and finance.In the provided exercise, we encounter the function \(e^{4t}\). Integrating this function involves recognizing that multiplying by the constant \(4\) means our integral, \(\int e^{4t} \, dt\), equals \(\frac{1}{4} e^{4t} + C\). In integration by parts, exponential functions often serve the role of \(dv\) due to their simplistic integral solutions.
Algebraic Functions
Algebraic functions are constructed using algebraic operations, which include addition, subtraction, multiplication, division, and taking roots. These functions are typically expressed in polynomial forms, like \(t^2\), \(3x^5\), or \(\sqrt{x}\).In integration by parts, algebraic functions are usually chosen as \(u\) because differentiating them simplifies the problem. Differentiating a polynomial reduces its degree, making it simpler to handle in subsequent steps.In the given problem, the algebraic function \(t^2\) serves as \(u\). Its differentiation, \(du = 2t \, dt\), reduces the degree of \(t\) from \(t^2\) to \(t\), thus simplifying the integration process. This reduction is essential in tandem with the application of the integration by parts formula, assisting in gradually resolving the integral into simpler components.

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Most popular questions from this chapter

Use a CAS to perform the integrations. Evaluate the integrals $$\text { a. } \int \frac{\ln x}{x^{2}} d x \quad \text { b. } \int \frac{\ln x}{x^{3}} d x \quad \text { c. } \int \frac{\ln x}{x^{4}} d x$$ d. What pattern do you see? Predict the formula for $$\int \frac{\ln x}{x^{5}} d x$$ and then see if you are correct by evaluating it with a CAS. e. What is the formula for $$\int \frac{\ln x}{x^{n}} d x, \quad n \geq 2 ?$$ Check your answer using a CAS.

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