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1.7.08 Teaching Example: Example 5
正文

  There is a sequence

, , , ,

Find .

  Solution: Assume that the sequence is a recursive sequence. The existence of the limit of such a sequence is often judged by the monotonic bounded criterion. For this question, obviously, there are

,

Therefore, the sequence increases monotonically.

  The following uses mathematical induction to prove that the sequence is bounded:

  Because , assuming , then we have

.

Therefore is bounded. According to criterion II, exists.

  Suppose , we know from the sign preservation property of the limit of the sequence, , because

,

Right now

,

Therefore, taking the limits on both ends of the above equation , we get

,

Right now

,

Solving the above quadratic equation, we get

or ( reject ) .

so

.

  For the graphics experiment of this example, see Experiment 1.9 of §1.3 .

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