Question

Find the sum of the first 16 terms of the arithmetic sequence: 8,11,14,17,20,...

Answer 1

S₁₆ = 488

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 = 8 and d = a₂ - a₁ = 11 - 8 = 3 , then

S₁₆ =
`(16)/(2)` [ (2 × 8) + (15 × 3) ]

= 8(16 + 45)

= 8 × 61

= 488