Sequence Listing

In this article, we are going to see about the sequence listing. There are two types of sequences

1. Arithmetic sequence and

2. Geometric sequence.

Arithmetic sequence means, the sequence of numbers such that the difference between two consecutive members of the sequence is a constant. Geometric sequence means, the sequence of numbers such that the ratio between two consecutive members of the sequence is a constant. The sequence listing formulas and example problems are given below.



Formula for arithmetic sequence:

nth term of the sequence : an = a1 + (n - 1)d

Series of the sequence: sn = (n(a_1 + a_n))/2

Formula for geometric sequence:

nth term of the sequence: an = a1 * rn-1

Series of the sequence: sn = (a_1(1-r^n))/(1 - r)
Example Problems for Sequence Listing:

Example problem 1:

Find the 15th term of the series 2, 4, 6, 8, 10,. ....

Solution:

First term of the series, a1 = 2

Difference of two consecutive terms, d = 4 - 2 = 2

n = 15

The formula to find the nth term of an arithmetic series, a_n = a_1 + (n-1)d

So, the 15th term of the series 2, 4, 6, 8, 10....... = 2 + (15 - 1) 2

= 2 + 14 * 2

After simplify this, we get

= 2 + 28

= 30

So, the 15th term of the sequence 2, 4, 6, 8, 10,.... is 30

Series of the arithmetic sequence: sn = (n(a_1 + a_n))/2

 s_15 = [15(2 + 30)]/(2)

 s_15 = [15(32)]/(2)

 s_15 = (480)/(2)

After simplify this, we get

 s_15 = 240



Example problem 2:

Find out the 11th term of a geometric sequence if a1 = 4 and the common ratio (C.R) r = 2

Solution:

Use the formula a_n = a_1 * r^(n-1) that gives the nth term to find a_11 as follows

a_11 = a_1 * r^(11-1)

= 4 * (2)10

= 4 * 1024

After simplify this, we get

= 4096

The 11th term of a geometric sequence is

Series of the sequence: sn = (a_1(1-r^n))/(1 - r)

 s_11 = [4(1 - 2^11)]/(1 - 2)

= [4(-2048)]/(-1)

After simplify this, we get

s_11 = 8192

The above examples are helpful study of sequences listing.