Question

Find the sum of sequence,-8,-5,-2..7

Answer 1

Answer: -3

first term = a = -8

Common difference = d = -5-(-8) = 3

Last term = l = 7

An = a+(n-1) d

7 = -8+(n-1) 3

15 = (n-1) 3

5 = n-1

n = 6

so, total number of terms is 6

Sn = n/2 ( a+l )

S6 = 6/2 (-8+7)

= 3 (-1)

= -3

so, the sum of given sequence is -3