Flashcards : Infinite Series and Taylor Methods — 61 cartes

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1Question

What is an infinite sequence in mathematics?

Réponse

An ordered list of numbers indexed by positive integers or another integer set.

2Question

When does a sequence converge to a limit L?

Réponse

When its terms become arbitrarily close to L as n approaches infinity.

3Question

What happens if a sequence has no finite limit?

Réponse

The sequence diverges.

4Question

For which values of r does the sequence r^n converge?

Réponse

For all r with -1 < r ≤ 1.

5Question

What is the limit of the sequence r^n when -1 < r < 1?

Réponse

The limit is 0.

6Question

What is the limit of the sequence r^n when r = 1?

Réponse

The limit is 1.

7Question

What does the Monotonic Sequence Theorem state?

Réponse

Every bounded monotonic sequence converges.

8Question

Which monotonic sequences are guaranteed to converge?

Réponse

Increasing sequences bounded above and decreasing sequences bounded below.

9Question

How is an infinite series defined?

Réponse

By its partial sums.

10Question

When does an infinite series converge?

Réponse

When its partial sums approach a finite real number.

11Question

What is the formula for the nth partial sum?

Réponse

s_n = sum of a_i from i=1 to n.

12Question

When does the geometric series sum ar^(n-1) converge?

Réponse

When the absolute value of r is less than 1.

13Question

What is the sum of a convergent geometric series?

Réponse

a divided by (1 minus r).

14Question

What happens if the limit of a_n is nonzero or does not exist?

Réponse

The series sum a_n diverges.

15Question

What if a_n approaches zero in the series sum a_n?

Réponse

The test is inconclusive.

16Question

Does the harmonic series sum 1/n converge or diverge?

Réponse

It diverges even though its terms approach zero.

17Question

What conditions on f ensure sum a_n and integral of f share convergence?

Réponse

f must be continuous, positive, and decreasing on the relevant tail.

18Question

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

Réponse

It converges when p is greater than 1.

19Question

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

Réponse

It diverges when p is less than or equal to 1.

20Question

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

Réponse

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

21Question

What is the integral remainder bound for the series sum 1/n^3?

Réponse

R_n is at most 1 divided by 2 n squared.

22Question

How many terms guarantee error below 0.0005 for sum 1/n^3 using integral remainder?

Réponse

At least 32 terms guarantee the error is below 0.0005.

23Question

What happens if 0 ≤ a_n ≤ b_n and sum b_n converges?

Réponse

Sum a_n converges.

24Question

What happens if a_n ≥ b_n ≥ 0 and sum b_n diverges?

Réponse

Sum a_n diverges.

25Question

What does the limit comparison test say if limit of a_n/b_n is c with 0 < c < ∞?

Réponse

Sum a_n and sum b_n both converge or both diverge.

26Question

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

Réponse

Compare dominant powers of n and choose bounds for convergence or divergence.

27Question

What inequality holds if 0 ≤ a_k ≤ b_k for every k > n?

Réponse

Tail remainder R_n of sum a_k is at most tail T_n of sum b_k.

28Question

When does the alternating series sum (-1)^n b_n converge?

Réponse

It converges when b_n is decreasing and approaches zero.

29Question

What inequality bounds the remainder of an alternating series meeting test conditions?

Réponse

The remainder satisfies |R_n| ≤ b_{n+1}.

30Question

What defines absolute convergence of a series?

Réponse

Absolute convergence occurs when the sum of |a_n| converges.

31Question

What defines conditional convergence of a series?

Réponse

Conditional convergence occurs when sum a_n converges but sum |a_n| diverges.

32Question

What happens to the sum of an absolutely convergent series under rearrangement?

Réponse

Its sum remains the same after any rearrangement.

33Question

How does rearranging a conditionally convergent series affect its sum?

Réponse

Rearranging can change the sum of a conditionally convergent series.

34Question

What is the first step in classifying a series for convergence?

Réponse

Inspect the term limit.

35Question

Which tests are suggested for factorials and constant-to-n terms?

Réponse

The Ratio Test.

36Question

For which term form is the Root Test suggested?

Réponse

Terms of the form (b_n)^n.

37Question

Why is the Ratio Test not recommended for p-series?

Réponse

Because the ratio a_(n+1)/a_n tends to 1.

38Question

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

Réponse

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

39Question

How can new power-series representations be obtained?

Réponse

By substituting an expression for x into a known series and adjusting convergence conditions.

40Question

How is the derivative of a power series inside its radius of convergence expressed?

Réponse

The derivative equals the sum from n=1 to infinity of n c_n (x-a)^(n-1).

41Question

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

Réponse

The radius of convergence remains the same.

42Question

What is the coefficient of \((x-a)^n\) in a Taylor series centered at a?

Réponse

It is \(c_n=\frac{f^{(n)}(a)}{n!}\).

43Question

What is the formula for the nth Taylor polynomial centered at a?

Réponse

It is \(T_n(x)=\sum_{i=0}^{n}\frac{f^{(i)}(a)}{i!}(x-a)^i\).

44Question

When does a formal Taylor series equal the function?

Réponse

Only when the remainder \(R_n(x)\) approaches zero on the interval.

45Question

What does Taylor's Inequality state about the remainder \(R_n(x)\)?

Réponse

If \(|f^{(n+1)}(x)| \le M\), then \(|R_n(x)| \le \frac{M|x-a|^{n+1}}{(n+1)!}\).

46Question

What is the Maclaurin series formula for e^x?

Réponse

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

47Question

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

Réponse

The radius of convergence is infinite.

48Question

What is the Maclaurin series formula for sin x?

Réponse

sin x = sum from n=0 to infinity of (-1)^n x^(2n+1) divided by (2n+1)!.

49Question

What is the Maclaurin series formula for cos x?

Réponse

cos x = sum from n=0 to infinity of (-1)^n x^(2n) divided by (2n)!.

50Question

What is the radius of convergence for the Maclaurin series of sin x and cos x?

Réponse

Both have infinite radius of convergence.

51Question

What is the Maclaurin series formula for arctan x?

Réponse

arctan x = sum from n=0 to infinity of (-1)^n x^(2n+1) divided by (2n+1).

52Question

What is the Maclaurin series formula for ln(1+x)?

Réponse

ln(1+x) = sum from n=1 to infinity of (-1)^(n-1) x^n divided by n.

53Question

What is the radius of convergence for the Maclaurin series of arctan x and ln(1+x)?

Réponse

Both have radius of convergence equal to 1.

54Question

What is the first step to approximate with a Taylor polynomial?

Réponse

Choose a center a.

55Question

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

Réponse

T₁(x) = f(a) + f'(a)(x - a).

56Question

How can Taylor approximation error be estimated when a derivative bound is known?

Réponse

By applying Taylor's Inequality.

57Question

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

Réponse

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

58Question

What error bound was obtained for the second-degree Taylor polynomial of f(x) = x^(1/3) on [7,9]?

Réponse

|R₂(x)| < 0.0004.

59Question

What series is used to approximate (1 + x)^(-1/2) in relativistic kinetic energy?

Réponse

The binomial series.

60Question

What substitution is made in the binomial series for relativistic kinetic energy approximation?

Réponse

x = -v²/c².

61Question

What does relativistic kinetic energy approximate to when v is much less than c?

Réponse

Approximately (1/2)m₀v².

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