Part of CALC-01 — Limits & Continuity

Limits of Sequences and Recursive Definitions

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Sequence limits: lim(n->infinity) ana_n where n is a natural number. All limit laws apply. Key results:

  • lim(n->infinity) 1/nkn^k = 0 for k > 0
  • lim(n->infinity) rnr^n = 0 if |r| < 1, = 1 if r = 1, diverges if |r| > 1
  • lim(n->infinity) n^1n\frac{1}{n} = 1
  • lim(n->infinity) (1/n!) = 0
  • lim(n->infinity) (n!)^1n\frac{1}{n} = infinity

Sum-to-integral conversion (Riemann sums): lim(n->infinity) 1n\frac{1}{n} * sum(r=0 to n-1) frn\frac{r}{n} = integral from 0 to 1 of f(x) dx.

Example: lim(n->infinity) [1n+1\frac{1}{n+1} + 1n+2\frac{1}{n+2} + ... + 12n\frac{1}{2n}] = lim 1n\frac{1}{n} * sum(r=1 to n) 11+r/n\frac{1}{1 + r/n} = integral from 0 to 1 of 11+x\frac{1}{1+x} dx = ln(2).

Recursive sequences: If a_(n+1) = f(ana_n) and the sequence converges to L, then L = f(L). Solve this equation to find L. But first verify convergence (e.g., show the sequence is monotonic and bounded).

JEE Pattern: Riemann sum problems appear regularly. The key is recognizing the pattern 1n\frac{1}{n} * sum frn\frac{r}{n} and converting to an integral.

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