Question

Find the sum of the first 7 terms of the geometric sequence : 3,9,27,81,...

(with solution)

PA HELP POOO THANKSSSS

Answer 1

3279

Explanation:

The sum to n terms of a geometric sequence is

`S_(n)` =
`(a(r^n-1))/(r-1)`

where a is the first term and r the common ratio

Here a = 2 and r = a₂ ÷ a₁ = 9 ÷ 3 = 3 , then

S₇ =
`(3(3^7-1))/(3-1)` =
`(3(2187-1))/(2)` = 1.5 × 2186 = 3279