# Sequences, Induction and Probability

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Sequences, Induction and Probability

Aim #10-1: What are sequences?
Definition of a sequence: An infinite sequence {an} is a function whose domain is the set of positive integers. The function values or terms, of the sequences are represented by a1, a2, a3, a4, …an… Sequences whose domain consists only of the first n positive integers are called finite sequences.

Example 1: Write the first four terms of the sequence whose nth term or general term, is given:

Check for Understanding:
Write the first four terms of the sequence whose nth term or general term , is given:

What is a Recursive Formula?
A recursive formula defines the nth term of a sequence as a function of the previous term.

Example 2: Using a Recursive Formula
Find the first four terms of the sequence in which a1=5 and an=3an-1+2 for n >2 Solution: a1=5 first term a2=3(5) + 2= 17 a3 =3(17) + 2 = ___ Continue substituting previous term in 3an-1 to find next term.

Check for understanding:
Find the first four terms of the sequence in which a1=3 and an=2an-1+ 5 for n >2

What is Factorial Notation?
Products of consecutive positive integers can be expressed in a special notation, called factorial notation. Factorial notation: If n is a positive integer, the notation n! (read “factorial”) is the product of all positive integers from n down through 1. n! = n (n - 1)(n - 2)… 0!=(zero factorial), by definition, is 1.

Example 3: Finding Terms of a Sequence Involving Factorials
Write the first four terms of the sequence whose nth term is Solution: We need to find the first four terms of the sequence. To do so we replace each n, with 1, 2, 3, and 4.

Check for understanding:
Write the first four terms of the sequence whose nth term is

Example 4: Evaluating Fractions with Factorials
Evaluate each factorial expression:

Check for Understanding
Evaluate each factorial expression:

What is Summation Notation?
The sum of the first n terms of a sequence is represented by the summation notation where i is the index of summation, n is the upper limit of summation, and 1 is the lower limit of summation.

Example 5: Using Summation Notation
Expand and evaluate the sum:

Check for Understanding
Expand and evaluate the sum:

Example 6: Writing Sums Express each sum using summation notation.

What is a sequence? Give an example with your description. Explain how to write your terms of sequence if the formula for the general term is given. What is a recursive formula? Explain how to find n! if n is a positive integer. Explain the best way to evaluate without a calculator. What is the meaning symbol for summation? Give an example of how it can be used.

Aim #10-2: What is an arithmetic sequence?
An arithmetic sequence is a sequence in which each term after the first differs from the preceding term by a constant amount. The difference between consecutive terms is called the common difference of the sequence. The common difference is found by subtracting any term from the term that directly follows it.

What is the common difference?
142, 146, 150, 154, 158, … -5, -2, 1, 4, 7, … 8, 3, -2, -7, -12, …

What is the rule of the arithmetic sequence?

Example 2: Using the Formula
Find the eighth term of the arithmetic sequence whose first term is 4 and whose common difference is -7.

Check for Understanding:
Find the ninth term of the arithmetic sequence whose first term is 6 and whose common difference is -5.

Example 3: Using the Arithmetic Sequence

Check for Understanding:
Thanks to drive-thrus and curbside delivery, American are eating more meals behind the wheel. In 2004, we averaged 32 a la car meals increasing by approximately 0.7 meals per year. Write a formula for the nth term of the arithmetic sequence that models the average number of car meals n years after How many car meals will Americans average by the year ?

The Sum of the First n Terms
The sum of the first n terms of an arithmetic sequence, denoted by Sn and called the nth partial sum.

Example 4: Finding the Sum of n Terms
Find the sum of the first 100 terms of the arithmetic sequence: 1, 3, 5, 7, …. Solution: We use the formula for the general term of an arithmetic sequence to find the a100. What is the common difference? Then we can use the above formula to find the sum of the first 100 terms.

Check for Understanding:
Find the sum of the first 15 terms of the arithmetic sequence: 3, 6, 9,12, ...

Example 5: Using Sn to Evaluate a Summation
Find the following sum: Solution: You can evaluate the first four terms and the last term. Then you can use the Sn formula.

What is an arithmetic sequence? Give an example with your explanation. What is the common difference in an arithmetic sequence? Explain how to find the sum of the first n terms of an arithmetic sequence without having to add up all of the terms. Find the sum of the first 80 positive even integers. TEXT P. 969 PRECALCULUS BOOK PROB 42 ANS 160 IS 80 TH TERM , 6480 IS THE SUM

Aim #10-3: What is a geometric sequence?
A geometric sequence is a sequence in which you multiply a fixed number to obtain the next number in the sequence. The amount by which we multiply each time is called the common ratio of the sequence. The common ratio of a sequence can be found by dividing.

How do we find the common ratio?
Geometric sequence 5, 25, 125, 625, … 4, 8, 16, 32, 64, … 6, -12, 24, -48, 96, … -3, 1, -1/3, 1/9, … What is the common ratio?

Example 1: Writing the terms
Write the first 6 terms of the geometric sequence with the first term 6 and common ratio 1/3.

Check for Understanding:
Write the first 6 terms of the geometric sequence with the first term 12 and common ratio 1/2.

What is the general term for the geometric sequence?

Example 2: Using the formula
Find the eighth term of the geometric sequence whose first term is -4 and whose common ratio is -2.

Check for Understanding:
Find the seventh term of the geometric sequence whose first term is 5 and whose common ratio is -3.

The Sum of the First n Terms of a Geometric Sequence
The sum, Sn , of the first n terms of a geometric sequence is given by : in which a1 is the first term and r is the common ratio (r≠0)

Example 4: Finding the Sum of the First n Terms of a Geometric Sequence
Find the sum of the first 18 terms of the geometric sequence: 2, -8, 32, -128 Solution: Replace n with 18 Identify the common ratio Then evaluate the formula

Check for Understanding:
Find the sum of the first 9 terms of the geometric sequence: 2, -6, 18, -54, …

What is a geometric series?
An infinite sum of the form a1 + a1r + a1r2 + a1r3 + …a1r n-1+… with the first term a1 and the common ratio r is called an infinite geometric series. How can we determine which infinite geometric series have sums and which do not?

The Sum of an Infinite Geometric Series

Example 8: Finding the Sum of an Infinite Geometric Series

Check for Understanding:
Find the sum of the infinite geometric series: / 3+ 8/9 + …

What is the geometric sequence? Give an example with your explanation. What is the common ratio in a geometric sequence? Find the sum of the first 11 terms of the geometric sequence: 4, -12, 36, -108, … Find the sum of the first 14 terms of the geometric sequence: Prob. 28, 30 p. 983 precalc book

Aim #10-5: What is the binomial theorem?
Binomial is a polynomial with 2 terms.

Here we are going to provide a formula that provides a quick method of raising a binomial to a power.

The Binomial Theorem:

Example 1: Finding Binomial Coefficients

Example 2: Finding Binomial Coefficients

From the last example you should have notice that:

Example 3:Expanding a Binomial Using Pascal’s Triangle

Finding the Term

Guided Practice: Find the 6th term of (a + 2b) 8

More Guided Practice: Find the 5th term of (4a + 3b )7.