Let’s think!
•The SSGClub proposed a project on collecting
bottles to lessen the trash on our school. If the
officers can collect 25 bottles on the first day, 45
on the second day , 65 on the third day, and the
pattern continues, how many bottles can they
collect in the fifth day? How many bottles they
will collect in one week?
3.
Arithmetic Sequence
•Is anordered set of numbers
that have a common
difference between each
consecutive term.
4.
Common difference
• Itis the value between each successive number in
an arithmetic sequence.
• the formula to find the common difference of an
arithmetic sequence is: d = a(n) - a(n - 1)
• where a(n) is nth term in the sequence, and a(n - 1)
is the previous term or (n - 1)th term) in the
sequence.
Tell if thefollowing sequences is an arithmetic
sequence or NOT, if an arithmetic sequence find its
common difference.
• 1.) 2, 4, 6, 11, ....
• 2.) 7, 10, 13, 16, 19,…
• 3.) 4, 8, 16, 32, …
• 4.) 2, 6, 10, 14, …
• 5.) 2, 5, 10, 17, …
• 6.) 1, 8, 9, 16, …
• 7.) 2, 11, 20, 29, …
7.
Arithmetic Sequence
• Thenth term of an arithmetic sequence with first term a1
and common difference d is given by:
• an = a1 + d (n-1)
• where:
• an is the term that corresponds to nth
position,
• a1 is the first term; and
• d is the common difference
8.
Let’s apply!
• A.Find the 21st term of the arithmetic sequence: 6, 9, 12, 15,…
• Solution:
• a. From the sequence, 𝑎1 = 6 , d = 3, and n = 21.
• b. Using the formula, substitute these values.
• a21 = 6 + 3 (21 – 1)
• a21 = 6 + 3 (20)
• a21 = 6 + 60
• a21 = 66
• c. Thus, the 21st term is 66.
9.
Let’s apply!
• B.Find an for each of the following arithmetic sequence.
• 1. a1 = 5; d = 4 ; n = 11
• 2. a1 = 14; d = –3 ; n = 25
• 3. a1 = 12; d = ½; n = 16
• 4. –10, –6, –2, 2, 6, … n = 27
• 5. 3, 5/2, 2, 1/2 ,0,… n = 28
Examples:
• 1. Inthe arithmetic sequence: 7, 10, 13, 16, . . .; find n if an =
304.
• Solution:
• a. From the sequence, a1 = 7, d = 3, and an = 304.
• b. Using the formula, substitute these values.
• an = a1 + d (n-1)
• 304 = 7 + 3 (n – 1)
• 304 = 7 + 3n – 3
• 304 = 4 + 3n
• 300 = 3n
• n = 100
• c. Thus, 304 is the 100th term of the sequence.
Examples:
• B. Findthe first term in the arithmetic sequence where the 35th term is
687 and the common difference 14.
• Using arithmetic sequence formula,
• an = a1 + (n − 1)d
• 687 = a1 + (35 - 1)14
• 687 = a1 + (34)14
• 687 = a1 + 476
• a1 = 211
• Answer: The first term in the sequence is 211.
15.
Examples:
• C. The3rd term of an arithmetic sequence is 8 and the
16th term is 47. Find d, 𝑎1 and the 71st term.
• Solution: a. From the sequence, a3 = 8 and a16 = 47
• b. These imply that:
• a3 = a1 + d (3-1) a16 = a1 + d (16-1)
• 8 = a1 + d (3-1) 47 = a1 + d (16-1)
• 8 = a1 + 2d Eq. 1 47 = a1 + 15d Eq. 2