Question

Determine whether the sequence 15,13,11,9 is an arithmetic sequence if yes, identify the common difference.

Answer 1

The sequence is not an arithmetic sequence because. The n-term for an arithmetic sequence is:

`a_n\text{ = }a_1\text{ + }(n-1)d`

where d is the difference between two consecutive numbers. In this case d = 2. Because

15-13 = 2

13-11 = 2

11- 9 = 2

now, the first term for 15,13,11,9 is 15 = a_1, the second term would be:

`a_2\text{ = }a_1\text{ + }(2-1)d\text{ }`

that is equivalent to say:

`a_2\text{ = 15 + }(2)2=19\\e13\text{ }`

So we can conclude that 15,13,11,9 is not an arithmetic sequence.