Question

What is the sum of the first 17 terms of this arithmetic series? Use .

-28 + (-13) + 2 + 17 + ⋯

Answer 1

AP: -28 , -13 , 2 , 17 ....

a = -28

d = -13 + 28 = 15

`S_n =`n(2a + (n - 1)d)/2

= 17/2 × (-28 × 2 + (17 - 1)15)

= 17/2 × ( - 28 × 2 + 16 × 15 )

= 17 ( - 28 + 120 )

= 17 × 92

= 1564