Question

What is Sn for the arithmetic series with d = -4, an = 27, and n = 9?

Answer 1

`99`

Explanation:

We may use the formula for the sum to `n` terms of an arithmetic series :

`sum_(k=1)^n[a+(k-1)d]=n/2[2a+(n-1)d]`

`=9/2[(2)(27)+(9-1)(-4)]`

`=99`