Fourier Series and Trigonometric Series
37 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What type of function must be used for sine series expansion according to the given content?

  • A rational function
  • An even function
  • An odd function (correct)
  • A discontinuous function

What is the primary purpose of restricting results to a specific interval after applying Dirichlet to the extended function?

  • To limit the analysis only to the required interval. (correct)
  • To ensure continuity across all intervals.
  • To make the function periodic.
  • To ensure that the function remains odd.

In the context of cosine series expansion, what characteristic must the function possess?

  • It must be even and 2b periodic. (correct)
  • It needs to be defined only on odd intervals.
  • It must be odd and discontinuous.
  • It should not be locally integrable.

Why might a sine series expansion be preferred over a Fourier series expansion in some cases?

<p>Sine series expand only for odd functions. (C)</p> Signup and view all the answers

What is the value of $F_f(x)$ for a piecewise continuous function f on $[l; l]$?

<p>$\frac{f(x) + f(x)}{2}$ (C)</p> Signup and view all the answers

If f is continuous on E R, what is the relationship between $F_f(x)$ and f?

<p>$F_f(x) = f(x)$ for all $x \in E$ (C)</p> Signup and view all the answers

For the function $f(x) = x$ defined on $[l; l]$, what is the nature of f?

<p>f is periodic with period 2 (A)</p> Signup and view all the answers

What is the result of $b_n$ when calculating Fourier coefficients for an odd function?

<p>$b_n = 0$ for all n (A)</p> Signup and view all the answers

In the context of Fourier series, which of the following statements is true regarding the periodic function described?

<p>The function must be integrable over its period. (A)</p> Signup and view all the answers

What is the nature of the series represented by $\sum_{n=1}^{\infty} \frac{cos(nx) \sin(nx)}{n^2} + 5$?

<p>It is a trigonometric series. (A)</p> Signup and view all the answers

What is the form of the points of discontinuity for the function f(x)?

<p>2k, k ∈ Z (B)</p> Signup and view all the answers

What is the value of $a_0$ in the trigonometric series given?

<p>0 (D)</p> Signup and view all the answers

What is the period of the function $f(x)$ if the trigonometric series is convergent?

<p>Interval of length 2 (D)</p> Signup and view all the answers

On which interval is the function f(x) considered to be odd and periodic?

<p>[0, 1] (B)</p> Signup and view all the answers

Which of the following statements is true about the coefficient $b_n$ from the trigonometric series?

<p>$b_n$ can be expressed as $\frac{1}{2} \int_0^2 f(x) \sin(nx)dx$. (A)</p> Signup and view all the answers

What is the limit of f'(x) as x approaches 0 from the right?

<p>2 (B)</p> Signup and view all the answers

What is the formula used for Ff(x) for x in the interval (0, ∞)?

<p>$\sum_{n=1}^{\infty} \frac{sin(nx)}{n}$ (B)</p> Signup and view all the answers

What does uniform convergence of the trigonometric series imply about its coefficients?

<p>The coefficients can be derived directly from the function f over the interval. (C)</p> Signup and view all the answers

How is the series $\sum_{n=1}^{\infty} a_n \cos(nx) + b_n \sin(nx)$ structured in the context of its coefficients?

<p>The coefficients are determined from the integrals of the function f. (D)</p> Signup and view all the answers

What does the Dirichlet corollary imply about the behavior of function f(x) at the point 2?

<p>f(2) is discontinuous. (A)</p> Signup and view all the answers

In the context of the series, what does the notation $\sum_{n=1}^{\infty} (a_n \cos(nx) + b_n \sin(nx))$ signify?

<p>An infinite series representing a periodic function. (C)</p> Signup and view all the answers

What is necessary to apply Dirichlet's conditions for a Fourier series expansion of a function defined on an interval [0; b]?

<p>An extended function must be defined on R and periodic. (D)</p> Signup and view all the answers

For a function that is locally integrable and odd, what property of its Fourier coefficients can be inferred?

<p>Only sine coefficients are non-zero. (C)</p> Signup and view all the answers

What does S2 represent in the context of the presented Fourier series expansion?

<p>The sum of all even Fourier coefficients. (A)</p> Signup and view all the answers

What is indicated by the periodicity of the function fe mentioned in the context?

<p>fe shares the same values as f within the interval [0; b]. (B)</p> Signup and view all the answers

When calculating S2 for an even function, what does the expression $\int_0^1 f^2(x)dx$ represent?

<p>The sum of squared Fourier coefficients. (D)</p> Signup and view all the answers

What is the significance of defining fe as even and 2b periodic for a cosine series expansion?

<p>It facilitates the application of Dirichlet's theorem. (B)</p> Signup and view all the answers

Which condition is NOT necessary for the function f when making a cosine series expansion?

<p>f must be differentiable on [0; b]. (C)</p> Signup and view all the answers

In the context of the Fourier series, what does the property of local integrability imply for the function f?

<p>f may possess discontinuities but has finite integrals over bounded intervals. (B)</p> Signup and view all the answers

What characterizes function f being of C1 piecewise on an interval [a, b]?

<p>The function can be expressed as a finite union of intervals. (C)</p> Signup and view all the answers

Which of the following series represents S1 when x is replaced with 0?

<p>$S1 = 0$ (B)</p> Signup and view all the answers

What is the condition for applying Dirichlet’s theorem as mentioned?

<p>f must be an even periodic function only in the interval [0, π]. (C)</p> Signup and view all the answers

What type of function behavior is suggested if both $\lim_{x \to x_i^+} f'(x)$ and $\lim_{x \to x_i^-} f'(x)$ exist and are finite?

<p>The function is likely continuous at x_i. (B)</p> Signup and view all the answers

What condition must hold for the function f to be considered integrable on any closed bounded interval of R?

<p>The function must have a finite number of discontinuities. (B)</p> Signup and view all the answers

In the Fourier series expansion, what series is used to express f(x)?

<p>$f(x) = \sum_{n=0}^{\infty} \frac{4 \cos((2n + 1)x)}{(2n + 1)}$ (B)</p> Signup and view all the answers

What does the term 2l periodicity imply about the function f?

<p>f is periodic with period 2. (C)</p> Signup and view all the answers

What is the significance of the expression $S2$ derived in the context?

<p>It connects two separate series into one expression. (B)</p> Signup and view all the answers

Flashcards

Trigonometric Series

A series involving trigonometric functions, like sine and cosine, with coefficients that depend on the index 'n'.

Normal Convergence of Trigonometric Series

A trigonometric series is said to be normally convergent on a set if the series of absolute values of its terms converges uniformly on that set.

Coefficients in Trigonometric Series

The coefficients 'an' and 'bn' in a trigonometric series determine the amplitude and phase of each harmonic component.

Periodicity of Convergent Trigonometric Series

If a trigonometric series converges to a function, that function is guaranteed to be periodic with a period of 2π.

Signup and view all the flashcards

Expression of Coefficients in Uniformly Convergent Trigonometric Series

The coefficients of a uniformly convergent trigonometric series can be calculated using definite integrals involving the function it represents.

Signup and view all the flashcards

Coefficient 'a0' in Trigonometric Series

The term 'a0' in the formula for the coefficients of a trigonometric series represents the average value of the function over a period.

Signup and view all the flashcards

Coefficient 'an' in Trigonometric Series

The coefficient 'an' in the formula for the coefficients of a trigonometric series represents the amplitude of the cosine component of the function at frequency 'n'.

Signup and view all the flashcards

Coefficient 'bn' in Trigonometric Series

The coefficient 'bn' in the formula for the coefficients of a trigonometric series represents the amplitude of the sine component of the function at frequency 'n'.

Signup and view all the flashcards

Piecewise Continuously Differentiable Function

A function f is piecewise continuously differentiable on an interval [a, b] if the interval can be divided into a finite number of subintervals where f is continuously differentiable within each subinterval, and the left and right limits of the derivative exist at the endpoints of each subinterval.

Signup and view all the flashcards

Fourier Series

The Fourier series of a function f(x) is an infinite series of sines and cosines that attempts to represent the function over its period. The coefficients of the series are determined by the function's behavior.

Signup and view all the flashcards

Dirichlet's Theorem

Dirichlet's theorem states that if f(x) is a periodic function that is piecewise continuously differentiable, then its Fourier series converges to the average of the left and right limits of f(x) at each point.

Signup and view all the flashcards

Fourier Cosine Coefficient

The coefficient of the nth cosine term in the Fourier series expansion of a function.

Signup and view all the flashcards

nth Harmonic

The nth harmonic of a periodic function in its Fourier series representation. It is characterized by its frequency, which is n times the fundamental frequency.

Signup and view all the flashcards

Fundamental Frequency

The fundamental frequency of a periodic function in its Fourier series representation. It is the lowest frequency present in the series.

Signup and view all the flashcards

C1 Piecewise Function

A function 'f' is considered 'C1 piecewise' on an interval if it is differentiable and its derivative is continuous in each subinterval of the interval, except at a finite number of points where the derivative might have jump discontinuities.

Signup and view all the flashcards

Fourier Transform (Ff(x))

The Fourier transform of a function 'f', denoted as 'Ff(x)', is a mathematical operation providing frequency domain information of the function. It decomposes the original function into its constituent frequencies.

Signup and view all the flashcards

Convergence of Fourier Transform for C1 Piecewise Functions

The Fourier transform of a function 'f', under certain conditions, is convergent to the average of the function's right and left-hand limits at a point 'x'. It provides a way to 'smooth out' the function.

Signup and view all the flashcards

Fourier Transform of a Continuous Function

If a function 'f' is continuous on a set 'E', then its Fourier transform 'Ff(x)' is equal to the function itself for all points in 'E'.

Signup and view all the flashcards

Fourier Coefficients (an, bn)

The Fourier coefficients are a set of numbers that represent the amplitude (strength) of each frequency component in a periodic function's Fourier series representation.

Signup and view all the flashcards

Fourier Series Expansion

The process of representing a function as an infinite sum of sines and cosines, allowing us to analyze and understand the function in terms of its frequency components.

Signup and view all the flashcards

Function Extension

The process of extending the definition of a function defined on a limited interval to a larger interval, making it periodic and allowing the Fourier series to be applied.

Signup and view all the flashcards

Parseval's Theorem

A theorem used to calculate the coefficients of a Fourier series by integrating the function multiplied by appropriate trigonometric functions.

Signup and view all the flashcards

Locally Integrable Function

A function is considered locally integrable over an interval if it is integrable within any smaller subinterval. Essentially, the function doesn't have any infinite 'jumps' or 'spikes' that make it impossible to integrate.

Signup and view all the flashcards

Cosine Series Expansion

Transforming a function into an equivalent representation that uses only cosine terms. The process involves applying Dirichlet's theorem and considering only the even extension.

Signup and view all the flashcards

Study Notes

Fourier Series

  • Fourier series represent periodic functions as an infinite sum of sine and cosine terms.
  • A function f is periodic if there exists a positive value T such that f(x + T) = f(x) for all x.
  • The smallest positive T is the fundamental period.

Trigonometric Series (Period 2π)

  • A trigonometric series is a series of functions of the form:
  • u₀(x) = α₀/2
  • uₙ(x) = aₙ cos(nx) + bₙ sin(nx) for n ≥ 1
  • Coefficients aₙ and bₙ are real numbers.

Convergence of Trigonometric Series

  • If both Σ|aₙ| and Σ|bₙ| converge, the trigonometric series converges normally (and thus uniformly) on ℝ to a continuous function.

Periodicity of Convergent Series

  • If a trigonometric series converges to a function f, then f is periodic with period 2π.

Coefficients on [0, 2π]

  • If a trigonometric series converges uniformly to a function f, its coefficients are given by:
  • α₀ = (1/π) ∫₀^(2π) f(x) dx
  • aₙ = (1/π) ∫₀^(2π) f(x) cos(nx) dx for n ≥ 1
  • bₙ = (1/π) ∫₀^(2π) f(x) sin(nx) dx for n ≥ 1

Fourier Series Expansion (Period 2π)

  • Let f be a real-valued function defined on ℝ with period 2π, integrable on any closed interval.
  • The Fourier series of f is given by:
  • Ff(x) = α₀/2 + Σ[aₙcos(nx) + bₙsin(nx)] for n ≥ 1
  • where α₀, aₙ, and bₙ are Fourier coefficients.

Parity and Fourier Coefficients

  • If f is an even function (f(-x)=f(x)), its Fourier coefficients satisfy aₙ = 0 and bₙ = (2/π)∫₀^π f(x)sin(nx) dx for any n ≥1.
  • If f is an odd function (f(-x)=-f(x)), its Fourier coefficients satisfy α₀ = 0 and aₙ = 0, bₙ=(2/π)∫₀^π f(x)sin(nx) dx for any n ≥1.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Fourier Series PDF

Description

Explore the concepts of Fourier series and trigonometric series, focusing on periodic functions and their representation as infinite sums of sine and cosine terms. Understand the conditions for convergence and determine the coefficients of the series within a given interval.

More Like This

Fourier Series Quiz
5 questions
Fourier Series Quiz
6 questions

Fourier Series Quiz

ProdigiousGrowth avatar
ProdigiousGrowth
Fourier Series Application and Analysis
5 questions
Use Quizgecko on...
Browser
Browser