Skip to main content
Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 7, Problem 7.6.65

Evaluate the integrals in Exercises 53–76.
65. ∫3dr/√(1-4(r-1)²)

Verified step by step guidance
1
Recognize that the integral has the form \( \int \frac{3 \, dr}{\sqrt{1 - 4(r-1)^2}} \), which resembles the standard integral \( \int \frac{dx}{\sqrt{a^2 - x^2}} = \arcsin\left(\frac{x}{a}\right) + C \).
Make a substitution to simplify the expression inside the square root. Let \( u = r - 1 \), so that \( du = dr \). The integral becomes \( \int \frac{3 \, du}{\sqrt{1 - 4u^2}} \).
Rewrite the expression under the square root as \( 1 - (2u)^2 \), which suggests another substitution or recognizing \( a = 1 \) and \( x = 2u \).
To match the standard form, factor out the constant inside the square root: \( \sqrt{1 - 4u^2} = \sqrt{1 - (2u)^2} \). Consider substituting \( w = 2u \), so \( dw = 2 du \) or \( du = \frac{dw}{2} \).
Rewrite the integral in terms of \( w \) and use the standard arcsine integral formula: \( \int \frac{dw}{\sqrt{1 - w^2}} = \arcsin(w) + C \). After integrating, substitute back \( w = 2u \) and \( u = r - 1 \) to express the answer in terms of \( r \).

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
3m
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Integration of Functions Involving Square Roots

This concept involves integrating functions that contain square roots, often requiring substitution or recognizing standard integral forms. Understanding how to manipulate the integrand to match known integral formulas is essential for solving these problems.
Recommended video:
07:01
Integrals Involving Natural Logs: Substitution

Trigonometric Substitution

Trigonometric substitution is a technique used to simplify integrals involving expressions like √(a² - x²), √(x² - a²), or √(a² + x²). By substituting x with a trigonometric function, the integral becomes easier to evaluate using trigonometric identities.
Recommended video:
6:04
Introduction to Trigonometric Functions

Definite and Indefinite Integrals

Understanding the difference between definite and indefinite integrals is crucial. Indefinite integrals represent families of functions plus a constant, while definite integrals compute the net area under a curve between limits. This problem involves an indefinite integral, focusing on finding the antiderivative.
Recommended video:
05:43
Definition of the Definite Integral