Question

Find sn for the arithmetic series where a1= 5 , n= 10, an= −13

Answer 1

S₁₀ = - 40

Explanation:

given the first term a₁ = 5 and the nth term
`a_(n)` = - 13

then the sum to n terms is

`S_(n)` =
`(n)/(2)` (a₁ +
`a_(n)` )

here n = 10 , then

S₁₀ =
`(10)/(2)` (5 + (- 13)) = 5(5 - 13) = 5 × - 8 = - 40