Question

What is the s10 for arithmetic sequence 25,20,15,10

Answer 1

S₁₀ = 25

Explanation:

the sum to n terms of an arithmetic sequence is

`S_(n)` =
`(n)/(2)` [ 2a₁ + (n - 1)d ]

where a₁ is the first term and d the common difference

here a₁ = 25 and d = a₂ - a₁ = 20 - 25 = - 5 , then

S₁₀ =
`(10)/(2)` [ (2 × 25) + (9 × - 5)]

= 5(50 - 45)

= 5 × 5

= 25