Flashcard: Infinite Sequences and Series — 68 carte

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1Domanda

What is an infinite sequence in mathematics?

Risposta

An ordered list of numbers indexed by specified positive integers.

2Domanda

What does the notation \(a_n \to L\) as \(n \to \infty\) signify?

Risposta

The terms get arbitrarily close to \(L\) for large \(n\).

3Domanda

What does a finite limit imply about a sequence?

Risposta

That the sequence converges.

4Domanda

When does the sequence \(\{r^n\}\) converge?

Risposta

Precisely when \(-1 < r \leq 1\).

5Domanda

What is the limit of \(\{r^n\}\) if \(-1 < r < 1\)?

Risposta

The limit is zero.

6Domanda

What is the limit of \(\{r^n\}\) when \(r = 1\)?

Risposta

The limit is one.

7Domanda

What does the Monotonic Sequence Theorem state about bounded monotonic sequences?

Risposta

They always converge.

8Domanda

What types of bounded monotonic sequences does the Monotonic Sequence Theorem specify?

Risposta

Increasing sequences bounded above or decreasing sequences bounded below.

9Domanda

What defines an infinite series in terms of partial sums?

Risposta

An infinite series is defined by its partial sums $s_n=\sum_{i=1}^n a_i$.

10Domanda

When does an infinite series converge?

Risposta

It converges when its partial sums approach a finite real number.

11Domanda

What is the sum formula for a geometric series with $|r|<1$?

Risposta

The sum is $\frac{a}{1-r}$.

12Domanda

What condition on $r$ ensures convergence of a geometric series?

Risposta

The series converges if $|r|<1$.

13Domanda

What does the Test for Divergence state about $\lim_{n\to\infty} a_n$?

Risposta

If the limit does not exist or is not zero, the series diverges.

14Domanda

What happens to a series if $\lim_{n\to\infty} a_n$ is not zero?

Risposta

The series diverges by the Test for Divergence.

15Domanda

Does the harmonic series $\sum_{n=1}^\infty \frac{1}{n}$ converge?

Risposta

No, the harmonic series diverges.

16Domanda

Do the terms of the harmonic series approach zero?

Risposta

Yes, its terms approach zero.

17Domanda

When does the Integral Test apply to a series?

Risposta

When a_n = f(n) with f continuous, positive, and decreasing on the tail.

18Domanda

What does the Integral Test conclude about series and integrals?

Risposta

The series and integral either both converge or both diverge.

19Domanda

When does the p-series ∑ 1/n^p converge?

Risposta

It converges when p > 1.

20Domanda

When does the p-series ∑ 1/n^p diverge?

Risposta

It diverges when p ≤ 1.

21Domanda

What inequality bounds the remainder R_n for a convergent positive decreasing series?

Risposta

∫_{n+1}^∞ f(x) dx ≤ R_n ≤ ∫_n^∞ f(x) dx.

22Domanda

How many terms are needed for ∑ 1/n^3 to have error below 0.0005?

Risposta

At least 32 terms are needed.

23Domanda

What remainder bound is used for ∑ 1/n^3 to estimate error?

Risposta

R_n ≤ 1/(2n^2).

24Domanda

When does Direct Comparison prove convergence for positive terms?

Risposta

When 0 ≤ a_n ≤ b_n and ∑b_n converges.

25Domanda

When does Direct Comparison prove divergence for positive terms?

Risposta

When a_n ≥ b_n ≥ 0 and ∑b_n diverges.

26Domanda

What condition must hold for Limit Comparison to apply to positive-term series?

Risposta

The limit of a_n/b_n as n→∞ equals a finite positive constant c.

27Domanda

What conclusion does Limit Comparison give about two series with positive terms?

Risposta

They have the same convergence behavior.

28Domanda

How do you compare rational or algebraic terms to a known p-series?

Risposta

By comparing dominant powers of n using Direct or Limit Comparison.

29Domanda

What inequality relates remainders of series when 0 ≤ a_k ≤ b_k for large k?

Risposta

The remainder of the a_k series is no larger than that of the b_k series.

30Domanda

When does the Alternating Series Test prove convergence?

Risposta

When the terms decrease and approach zero.

31Domanda

What inequality bounds the remainder in an alternating series satisfying the test?

Risposta

The remainder's absolute value is at most the next term's magnitude.

32Domanda

What defines absolute convergence of a series?

Risposta

The series of absolute values converges.

33Domanda

What defines conditional convergence of a series?

Risposta

The series converges but its absolute value series diverges.

34Domanda

What does absolute convergence imply about ordinary convergence?

Risposta

Absolute convergence implies ordinary convergence.

35Domanda

What is true about rearrangements of absolutely convergent series?

Risposta

They all have the same sum.

36Domanda

What is the first step in selecting a convergence test?

Risposta

Inspect the term limit.

37Domanda

Which series forms should you check after the term limit?

Risposta

P-series or geometric form.

38Domanda

What should you inspect after checking for p-series or geometric form?

Risposta

Signs and algebraic structure.

39Domanda

Which test is suggested for factorials, products, or constant-to-the-n terms?

Risposta

The Ratio Test.

40Domanda

For which term form is the Root Test suggested?

Risposta

Terms of the form (b_n)^n.

41Domanda

Why is the Ratio Test not useful for many rational or p-series terms?

Risposta

Because a_{n+1}/a_n tends to 1.

42Domanda

What is the geometric series identity for |x|<1?

Risposta

1/(1-x) equals the sum from n=0 to infinity of x^n.

43Domanda

What series results from substituting -x^2 into the geometric series?

Risposta

1/(1+x^2) equals the sum from n=0 to infinity of (-1)^n x^{2n}.

44Domanda

What operation can be done term by term inside a power series' radius of convergence?

Risposta

A power series can be differentiated or integrated term by term inside its radius of convergence.

45Domanda

What happens to the radius of convergence after term-by-term differentiation or integration?

Risposta

The resulting series has the same radius of convergence.

46Domanda

What is the domain of the Bessel-function power series example?

Risposta

Its domain is all real numbers because it converges for every real x.

47Domanda

Can the Bessel-function power series be differentiated term by term?

Risposta

Yes, it can be differentiated term by term.

48Domanda

What is the formula for the coefficient in a Taylor series centered at a?

Risposta

It is c_n = f^(n)(a) divided by n!

49Domanda

How is the Taylor series centered at a expressed as a sum?

Risposta

As the sum from n=0 to infinity of (f^(n)(a)/n!) times (x - a)^n

50Domanda

What defines a Maclaurin series in relation to a Taylor series?

Risposta

It is a Taylor series centered at a = 0

51Domanda

How is a Maclaurin series written as a sum?

Risposta

As the sum from n=0 to infinity of (f^(n)(0)/n!) times x^n

52Domanda

What is the nth-degree Taylor polynomial T_n(x)?

Risposta

It is the finite sum from i=0 to n of (f^(i)(a)/i!) times (x - a)^i

53Domanda

Does the nth-degree Taylor polynomial always equal the function?

Risposta

No, it need not equal the function

54Domanda

When does a function equal its Taylor series on an interval?

Risposta

Only when the remainder R_n(x) approaches zero there

55Domanda

What is the remainder R_n(x) in Taylor series approximation?

Risposta

It is f(x) minus the nth-degree Taylor polynomial T_n(x)

56Domanda

What is the Maclaurin series formula for the exponential function?

Risposta

It is e^x = sum from n=0 to infinity of x^n divided by n!.

57Domanda

What is the radius of convergence for the Maclaurin series of e^x?

Risposta

The radius of convergence is infinite.

58Domanda

What radius of convergence do sin x and cos x have in their standard series?

Risposta

They have an infinite radius of convergence.

59Domanda

What radius of convergence do arctan x and ln(1+x) have in their standard series?

Risposta

They have a radius of convergence equal to 1.

60Domanda

What is the binomial series formula for (1+x)^k?

Risposta

It is (1+x)^k = sum from n=0 to infinity of binomial(k,n) times x^n.

61Domanda

How is the binomial coefficient binomial(k,n) defined for the binomial series?

Risposta

It is k(k-1)...(k-n+1) divided by n!.

62Domanda

What is the domain condition for the binomial series (1+x)^k to converge?

Risposta

It converges for |x| less than 1.

63Domanda

Name methods to generate new series from known series.

Risposta

Substitution, multiplication, term-by-term differentiation or integration, formal multiplication, and power-series long division.

64Domanda

What is the formula for the linear Taylor approximation T₁(x)?

Risposta

T₁(x) = f(a) + f'(a)(x - a).

65Domanda

What does Taylor’s Inequality bound in terms of the remainder Rₙ(x)?

Risposta

|Rₙ(x)| ≤ (M|x - a|^{n+1}) / (n+1)! when |f^{(n+1)}(x)| ≤ M.

66Domanda

What is the second-degree Taylor polynomial for f(x) = x^{1/3} at a = 8?

Risposta

T₂(x) = 2 + (1/12)(x - 8) - (1/288)(x - 8)^2.

67Domanda

What error bound is given for the cube-root approximation on 7 ≤ x ≤ 9 using M = 0.0021?

Risposta

|R₂(x)| < 0.0004.

68Domanda

What classical approximation results from expanding relativistic kinetic energy for v ≪ c?

Risposta

K ≈ (1/2) m₀ v².

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1. What distinguishes a sequence from a series?

2. What does the statement $a_n\to L$ as $n\to\infty$ mean?

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