Question

What is the sum of the geometric sequence −1, 6, −36, … if there are 7 terms?

Answer 1

first work out the common ratio = second term / first term

Answer 2

ok so would that be 6?

Answer 3

6 / -1 = -6

Answer 4

Yes, sorry :)

Answer 5

then use the formula for sum of n terms

Sn = a1 * (1 - r^n)
----------
1 - r

where a1 = first term and r = common ratio, n = number of terms

Answer 6

Hmm then you would plug that in to get -39,991?