What is the sum of the geometric sequence -3, 18, -108, … if there are 7 terms?
3 Answers
Aug 14, 2018
Explanation:
"the sum to n terms for a geometric sequence is"
•color(white)(x)S_n=(a(r^(n-1)))/(r-1)
"where a is the first term and r the common ratio"
a=-3" and "r=(-108)/18=18/(-3)=-6
S_7=(-3((-6)^7-1))/(-6-1)
color(white)(xx)=(-3(-279936-1))/(-7)
color(white)(xx)=(-3xx-279937)/(-7)=-19973
Aug 14, 2018
Explanation:
Here,
Let ,first term
common ratio
So, the sum of first n terms is:
Aug 14, 2018
-119973
Explanation:
We can first see that the ratio between these is