What is the sum of the first seven terms of the geometric series 3 − 6 + 12 − . . . ?

Hint: Sn= a1(1-rn)/1-r, r ≠ 1, where a1 is the first term and r is the common ratio.

Question

What is the sum of the first seven terms of the geometric series 3 − 6 + 12 − . . . ?

Hint: Sn= a1(1-rn)/1-r, r ≠ 1, where a1 is the first term and r is the common ratio.

jim_thompson5910 · Answer

Another hint: 

$\Large a_1 = 3$ is the first term
$\Large r = -2$ is the common ratio (you multiply each term by -2 to get the next term)
$\Large n = 7$ is the number of terms you are summing up