/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 64 Use reduction formulas to evalua... [FREE SOLUTION] | 91Ó°ÊÓ

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Use reduction formulas to evaluate the integrals. \(\int 4 \cot ^{3} 2 t d t\)

Short Answer

Expert verified
The integral evaluates to \(-2\csc(2t) - 2\ln|\sin(2t)| + C\)."

Step by step solution

01

Understand the Integral

Recognize that the integral involves the function \(\cot^{3}(2t)\), which is not straightforward to integrate directly. We need to simplify or decompose this function using identities or reduction formula techniques.
02

Use Trigonometric Identity for Cotangent

Recall that \(\cot^2(x) + 1 = \csc^2(x)\). Use this identity to rewrite \(\cot^{3}(x)\) as \(\cot(x)\cot^2(x) = \cot(x)(\csc^2(x) - 1)\). Thus, rewrite the integral:
03

Rewrite the Integral Expression

The integral becomes:\[\int 4 \cot^{3}(2t) \, dt = \int 4 \cot(2t)(\csc^2(2t) - 1) \, dt\]This splits into two separate integrals:\[4 \int \cot(2t) \csc^2(2t) \, dt - 4 \int \cot(2t) \, dt\]
04

Solve the First Integral

For \(\int \cot(2t) \csc^2(2t) \, dt\), recognize the derivative form. Since \(\frac{d}{dt}[-\csc(2t)] = -2 \cot(2t) \csc(2t)\), we recognize the integral differs by a factor and find:\[\int \cot(2t) \csc^2(2t) \, dt = -\frac{1}{2} \csc(2t)\]
05

Solve the Second Integral

For \(\int \cot(2t) \, dt\), use the fact that the integral is a standard form:\[\int \cot(2t) \, dt = \frac{1}{2} \ln|\sin(2t)| + C\]
06

Combine Results

Substitute the results of the integrals back into the original expression:\[\int 4 \cot^{3}(2t) \, dt = 4\left(-\frac{1}{2} \csc(2t)\right) - 4\left(\frac{1}{2} \ln|\sin(2t)|\right) + C\]Simplifying gives:\[-2 \csc(2t) - 2 \ln|\sin(2t)| + C\]
07

Final Simplification and Presentation

The final expression for the integral is:\[-2 \csc(2t) - 2 \ln|\sin(2t)| + C\]

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Key Concepts

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

Trigonometric Integrals
Trigonometric integrals involve integrating functions that include trigonometric functions such as sine, cosine, tangent, cotangent, secant, and cosecant. In many calculus problems, you will encounter integrals with these functions, and knowing how to manipulate them is crucial.

These types of integrals are often solved using special techniques or identities to simplify the expression before integrating. For example, the integration problem in the original exercise involves the function \( \cot^3(2t) \). This isn't easy to integrate directly, which is why it's important to use trigonometric identities to rewrite and simplify the function first.

  • Breaking down complex trigonometric functions into simpler components can make them easier to integrate.
  • Techniques for integrating trigonometric functions often use identities like \( \sin^2(x) + \cos^2(x) = 1 \), or, in our example, \( \cot^2(x) + 1 = \csc^2(x) \).
Mastering trigonometric integrals requires patience and practice, along with a good grasp of trigonometric identities.
Reduction Formulas
Reduction formulas are special types of identities used to simplify complex integrals into more manageable forms. They are especially helpful for repeated or higher power trigonometric functions. These formulas allow you to express a complex integral in terms of a simpler one, often reducing the power of the trigonometric function by one or more steps.

In our original exercise, the power of \( \cot(2t) \) needed to be reduced for easier integration. By using the identity:\[\cot^2(x) + 1 = \csc^2(x)\]we could transform \( \cot^{3}(2t) \) into a combination of simpler expressions that can be integrated separately.

Here's how reduction formulas help:
  • They simplify the integration process by reducing the trigonometric power.
  • Once transformed, different parts of the integral can be solved using known antiderivatives or identities.
This strategy greatly simplifies many complex integrals, making them feasible to solve without advanced techniques.
Cotangent and Cosecant Identities
Utilizing identities of cotangent and cosecant can be crucial when dealing with integrals, like in the given problem. Understanding these identities allows you to rewrite and simplify the terms for easier integration. The identity \( \cot^2(x) + 1 = \csc^2(x) \) was initially used to simplify \( \cot^{3}(2t) \).

This transformation enables breaking down the initial integral into parts, as seen in the original solution. By splitting \( \cot(2t)(\csc^2(2t) - 1) \), the integral was divided into simpler forms:\[4 \int \cot(2t) \csc^2(2t) \, dt - 4 \int \cot(2t) \, dt\]Each part became easier to solve using known derivatives or results, such as acknowledging the derivative of \( -\csc(x) \) or the integral of \( \cot(x) \) resulting in log terms.

This knowledge of identities helps:
  • Enhance understanding of trigonometric interactions and transformations.
  • Provide pathways through which complex integrals can be addressed systematically.
Getting comfortable with these identities builds foundational skills necessary to tackle intricate calculus problems.

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Most popular questions from this chapter

Evaluate the integrals in Exercises \(1-28\). $$ \int \frac{d x}{x^{2} \sqrt{x^{2}+1}} $$

Solve the initial value problems in Exercises \(37-40\) for \(y\) as a function of \(x .\) $$ x \frac{d y}{d x}=\sqrt{x^{2}-4}, \quad x \geq 2, \quad y(2)=0 $$

Usable values of the sine-integral function The sine-integral function, $$ \operatorname{Si}(x)=\int_{0}^{x} \frac{\sin t}{t} d t $$ is one of the many functions in engineering whose formulas cannot be simplified. There is no elementary formula for the antiderivative of \((\sin 1) / t\) . The values of \(\mathrm{Si}(x),\) however, are readily estimated by numerical integration. Although the notation does not show it explicitly, the function being integrated is $$ f(t)=\left\\{\begin{array}{cl}{\frac{\sin t}{t},} & {t \neq 0} \\ {1,} & {t=0}\end{array}\right. $$ the continuous extension of \((\sin t) / t\) to the interval \([0, x] .\) The function has derivatives of all orders at every point of its domain. Its graph is smooth, and you can expect good results from Simpson's Rule. a. Use the fact that \(\left|f^{(4)}\right| \leq 1\) on \([0, \pi / 2]\) to give an upper bound for the error that will occur if $$ \operatorname{Si}\left(\frac{\pi}{2}\right)=\int_{0}^{\pi / 2} \frac{\sin t}{t} d t $$ is estimated by Simpson's Rule with \(n=4\) . b. Estimate \(\operatorname{Si}(\pi / 2)\) by Simpson's Rule with \(n=4\) c. Express the error bound you found in part (a) as a percentage of the value you found in part (b).

Your engineering firm is bidding for the contract to construct the tunnel shown here. The tunnel is 300 \(\mathrm{ft}\) long and 50 \(\mathrm{ft}\) wide at the base. The cross-section is shaped like one arch of the curve \(y=25 \cos (\pi x / 50) .\) Upon completion, the tunnel's insides urface (excluding the roadway) will be treated with a waterproof sealer that costs \(\$ 1.75\) per square foot to apply. How much will it cost to apply the sealer? (Hint: Use numerical integration to find the length of the cosine curve.)

Use the integral tables to evaluate the integrals. \(\int x^{2} \cosh 3 x d x\)

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