Classify the series as arithmetic or geometric then determine whether the series is convergent or divergent

    Arithmetic , Divergent

Step-by-step explanation:

Given sequence is  

{aₙ} =  {  4 , 10/3  , 8/ 3 , 2 , . . .   }

To check whether the sequence is geometric or not , we divide second term by first term  to find the common ratio . Then we again divide third term by second term to get common ratio .

The common ratio we get would same , then it is geometric .

         10/3               10            5

r₁  =    =        =  

             4                12             6

        8/3                8                  3                4

r₂=     =    *     =    

           10/ 3             3              10                  5

Thus the common ratio are not same . So the sequence is not geometric .

Now we check for arithmetic .

We take difference of second and first term and then difference of third and second term . If it will be same then it is arithmetic . This is called common difference , d .

             10                       -  2

d₁   =         - 4   =      

              3                          3

                8            10             - 2

d₂   =        -      =  

               3             3                 3

Thus the common difference is same .

So the given sequence is arithmetic .

To find whether it is convergent or divergent , we need to write sum of n terms first .

Formula for finding sum of n terms of arithmetic sequence is

            n

sₙ =      [ 2a + ( n - 1 ) d]

             2

We have a = 4 , d = - 2/3 .

Plug  in this formula we get

              n                                                    n                2             2

sₙ  =     [ 2 * 4 + ( n - 1 ) ( -2/3) ]  =     [  8 -    n  +    ]

              2                                                    2                3               3

           n          26              2

sₙ  =    [        -     n  ]

           2           3                3

To check whether it is convergent or divergent , we take limit sₙ approaches to infinity .

                               n       26       2

lim   sₙ   =     lim    { ---   [  ---  -   n ] } =     - ∞

n → ∞           n→∞      2        3       3

As the sequence diverge , thus the series is divergent .

Thus given series is arithmetic , divergent .

Second is the  correct option .

the first one

step-by-step explanation:

just id the test.