Question

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

Answer 1

Answer:

$\sum_{x=1}^{4}(17-4n)$

Step-by-step 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

$\sum_{x=1}^{4}(17-4n)$

Answer 2

$13 + 9 + 5 + 1 = 27$