UCLA Math 31B: Fall 2024 Midterm 2
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Questions and Answers

Explain why knowing whether a sequence converges is useful in determining if an infinite series converges.

If the sequence of terms in an infinite series does not converge to zero, the series diverges, by the Divergence Test.

Describe the key difference between finding the limit of a sequence and finding the sum of a series.

A sequence involves finding the value the terms approach, while a series involves adding all the terms and finding the value of the sum.

Why is the comparison test useful for determining the convergence or divergence of improper integrals?

The comparison test helps because if an integral is bounded above or below by a convergent or divergent integral, respectively, its convergence can be determined.

Explain how the choice of the axis of revolution affects the integral setup for calculating the surface area of a solid of revolution.

<p>The axis of revolution determines the radius of the circular strip, which is a factor in the surface area integral. Different axes lead to different radii expressed in terms of (x) or (y).</p> Signup and view all the answers

Describe a scenario where integration by parts becomes particularly useful when evaluating definite integrals.

<p>It is particularly helpful when the integrand is a product of functions where one simplifies upon differentiation and the other is easily integrable.</p> Signup and view all the answers

Explain how the absolute value of (r) affects the convergence of a geometric series (\sum ar^n).

<p>The geometric series converges if the absolute value of (r) (the common ratio) is less than 1 (|r| &lt; 1), and diverges if the absolute value of (r) is greater than or equal to 1 (|r| ≥ 1).</p> Signup and view all the answers

Explain how the choice between using the disk/washer method versus the shell method can simplify the calculation of the volume of a solid of revolution.

<p>The choice depends on the orientation of the axis of revolution relative to the function. The shell method often simplifies integrals when integrating parallel to the axis of revolution.</p> Signup and view all the answers

How does the behavior of a function's derivative, (f'(x)), influence the arc length calculation?

<p>The derivative (f'(x)) is used in the arc length formula to account for the rate of change of the function, affecting the total length of the curve.</p> Signup and view all the answers

When determining the convergence of an alternating series, explain why it is important to check if the absolute value of the terms is decreasing.

<p>For an alternating series to converge, the absolute value of its terms must decrease and approach zero. This ensures the oscillations dampen out, allowing the series to converge to a finite value.</p> Signup and view all the answers

Explain how L'Hôpital's Rule helps in evaluating limits involving sequences. Give an example.

<p>L'Hôpital's Rule can be applied to the continuous analogue of a sequence (i.e., a function) when evaluating limits of indeterminate forms. If (\lim_{x \to \infty} f(x)/g(x)) is of the form 0/0 or ∞/∞, then (\lim_{x \to \infty} f(x)/g(x) = \lim_{x \to \infty} f'(x)/g'(x)). For example, finding the limit of the sequence (n/e^n) is the same as finding the limit of (x/e^x) as x approaches inifinity.</p> Signup and view all the answers

Flashcards

Arc Length Formula

The length of a curve y = f(x) from x = a to x = b is given by the integral of the square root of 1 plus the square of the derivative of f(x), integrated from a to b.

Surface Area of Revolution

The surface area (S) obtained by rotating the curve y = f(x) about the x-axis from x = a to x = b. It involves integrating 2π * f(x) * sqrt(1 + (f'(x))^2) from a to b.

arcsin Integral

∫ dx / √(a² - x²) = sin⁻¹(x/a) + C

arctan Integral

∫ dx / (x² + a²) = (1/a) * tan⁻¹(x/a) + C

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arcsec Integral

∫ dx / (x√(x² - a²)) = (1/a) * sec⁻¹(|x|/a) + C

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Complex Integral

∫ 1/(x√(x-3)(x-2)) dx

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Study Notes

  • The material is for UCLA Math 31B, Fall 2024, Midterm 2.
  • The exam is on Monday, November 18.
  • Instructor: David Beers

Exam Instructions and Rules

  • Points are deducted if work is not shown, unless the question states otherwise.
  • Answers must be written directly on the test, either on the front or back of the page where the question is written.
  • Calculators, notebooks, textbooks, headphones, and cheat sheets are prohibited.
  • Phones must be turned off and stored away during the exam.
  • Talking or writing is not allowed on the exam after time is up.
  • Violations of these rules result in a deduction of at least 25 points.

Derivative Formulas

  • d/dx sin⁻¹x = 1/√(1 - x²)
  • d/dx cos⁻¹x = -1/√(1 - x²)
  • d/dx tan⁻¹x = 1/(x² + 1)

Integral Formulas

  • ∫ dx/√(1 - x²) = sin⁻¹x + C
  • ∫ -dx/√(1 - x²) = cos⁻¹x + C
  • ∫ dx/(x² + 1) = tan⁻¹x + C

Arc Length

  • The arc length is given by: s = ∫√(1 + (f'(x))²) dx from a to b.

Surface Area

  • The surface area is given by: S = 2π ∫ f(x)√(1 + (f'(x))²) dx from a to b.

Convergence Determination

  • Determine the convergence of integrals, sequences, and series; no work required; each worth 5 points
  • ∫1/x dx from 1 to ∞
  • ∫1/x^(9/10) dx from 0 to 1
  • {(-1.5)^n}_(n=1 to ∞)
  • ∑ (-1)^n from n=0 to ∞
  • ∑ (1/n)^n from n=1 to ∞

Series Convergence and Value

  • Determine convergence/divergence of sequence/series and compute its convergence value, show work
  • Sequence {(-n/ln(n))^n} from n=2 to ∞ (12 points)
  • Series ∑ 2(2/3)^n from n=3 to ∞ (13 points)

Computations Required

  • Compute ∫ 1/sqrt((x-3)(x-2)) dx (12 points)
  • Given f(x) = x³, compute surface area of the revolution around the x-axis on [0, 1] (13 points)

Improper Integrals

  • Determine divergence/convergence of improper integrals; no computation needed, show work
  • ∫ e^(-x) / (e^(-x) + x) dx from 0 to 1 (12 points)
  • ∫ 1 / sqrt(x³ + x⁴) dx from 0 to 1 (13 points)

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Description

This material covers information for the UCLA Math 31B Midterm 2 exam in Fall 2024, instructed by David Beers. It includes exam instructions, derivative and integral formulas, and formulas for arc length and surface area. The exam is scheduled for Monday, November 18.

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