翻译
Monotonic sequences of real numbers
A sequences {f(n)} is said to be increasing if
f(n) f(n+1) for all n 1
We indicate this briefly by writeing
hand ,we have
f(n) f(n+1) for all n 1 f(n). if, on the other
We call the sequences decreasing and write f(n). .A sequences is called monotonic if it is increasing or if it is decreasing.
Monotonic sequences are pleasant to work with because their convergence or divergence is particularly easy to determine. In fact ,we have the following simple criterion.
Note:A sequences {f(n)} is called bounded if there exists a positive number M such that
f(n) M for all n. A sequences that is not bounded is called unbounded.
It is clear that an unbounded sequence cannot converge. Therefore, all we need to prove is that a bounded monotonic sequences must converge.
Assume f(n)and let L denote the least upper bound of
f(n) L the set of function values.then for all n, and we shall