Question

The given series has six terms. What is the sum of the terms of the series?

(–7) + (–9) + (–11) + . . . + (–17)

–32

–42

–72

–52

Answer 1

The given series is arithmetic.
We first get the number of terms in the series.

Tn = a+(n-1)d
-17 = -7 + (n-1)-2
-17 = -7 -2n+2
-17 +5 = -2n
n = 12/2
n = 6 

The sum of the series is given by Sn = n/2 (a+l)
Sn = 6/2 (-7+-17)
     = 3(-24) = -72