Question

7, 21,63, 189,...
Use the formula for the sum of the first n terms of a geometric system to solve this exercise. Find the sum of the first 11 terms.

Answer 1

looks like \(r=3\) so you have
\[7+7\times 3+7\times 3^2+...+7\times 3^{10}\]
\[=7(1+3+3^2+...+3^{10}\]
\[=7\frac{3^{11}-1}{3-1}\]

Answer 2

7, 21, 63, 189, 567, 1701, 5103, 15309, 45927, 137781 = 206668

Answer 3

you need eleven terms, not ten

Answer 4

oh my bad i read wrong.

Answer 5

620011 should be the total.