Question

Which summation formula represents the series below? 13 + 9 + 5 + 1

Answer 1

a

Explanation:

Answer 2

`\sum_(x=1)^(4)(17-4n)`

Explanation:

The given expression is

`13+9+5+1`

The terms of this series are

13,9,5,1

It is an AP. Here, first term is 13 and common ratio is -4.

The nth term of an AP is

`a_n=a+(n-1)d`

where, a is first term and d is common difference.

The nth term of given AP is

`a_n=13+(n-1)(-4)`

`a_n=13-4n+4`

`a_n=17-4n`

The summation formula of an AP is

`\sum_(x=1)^(n)a_n`

The value of n is 4 because the number of term is 4. So, the summation formula is

`\sum_(x=1)^(4)(17-4n)`