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# 11.E: Sequences, Probability and Counting Theory (Exercises)

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## 11.1 Sequences and Their Notations

### Verbal

1) Discuss the meaning of a sequence. If a finite sequence is defined by a formula, what is its domain? What about an infinite sequence?

A sequence is an ordered list of numbers that can be either finite or infinite in number. When a finite sequence is defined by a formula, its domain is a subset of the non-negative integers. When an infinite sequence is defined by a formula, its domain is all positive or all non-negative integers.

2) Describe three ways that a sequence can be defined.

3) Is the ordered set of even numbers an infinite sequence? What about the ordered set of odd numbers? Explain why or why not.

Yes, both sets go on indefinitely, so they are both infinite sequences.

4) What happens to the terms $$a_n$$ of a sequence when there is a negative factor in the formula that is raised to a power that includes $$n$$? What is the term used to describe this phenomenon?

5) What is a factorial, and how is it denoted? Use an example to illustrate how factorial notation can be beneficial.

A factorial is the product of a positive integer and all the positive integers below it. An exclamation point is used to indicate the operation. Answers may vary. An example of the benefit of using factorial notation is when indicating the product It is much easier to write than it is to write out $$13\cdot 12\cdot 11\cdot 10\cdot 9\cdot 8\cdot 7\cdot 6\cdot 5\cdot 4\cdot 3\cdot 2\cdot 1$$

### Algebraic

For the exercises 6-15, write the first four terms of the sequence.

6) $$a_n=2^n-2$$

7) $$a_n=-\dfrac{16}{n+1}$$

First four terms: $$-8$$,