to find the sum of a geometri sequence from first term to nth term you do
Sn=(n(a1+an))/2
a1=-82
n=10
hmm
common difference is 6 since adding 6 each time
first term is -82
10th term is -82+6(10-1)=-28
sum of 10 terms is
Sn=(10(-82-28))/2
Sn=(10(-110))/2
Sn=(-1100)/2
Sn=-550
answer is -550
