What is the sum of the geometric sequence -3, 18, -108, … if there are 7 terms?
3 Answers
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#
Explanation:
Here,
Let ,first term
common ratio
So, the sum of first n terms is:
-119973
Explanation:
We can first see that the ratio between these is