Question

4 + 12 + 36 + … ; n = 15

Answer 1

I've attached a picture below of the formula for a finite geometric sequence. It includes an infinite geometric sequence formula for your reference, too.


`a_1 = 4`

`r(ratio)= 3`

`n=15`

Plug in the values.


`S_(15) = 4*( (1-3^(15))/(1-3) )`

`S_(15) = 4*( (1-3^(15))/(-2) )`

`S_(15) = 4*( (1-14348907)/(-2) )`

`S_(15) = 4*( (-14348906)/(-2) )`

`S_(15) = 4*7174453`
S₁₅ = 28697812

Answer 2

4 times 3=12
12 times 3=36
I think you want us to find the sum of the geometric sequence to n=15

the sum is

`S= (a_1(1-r^(n)))/(1-r)`
a1=first term=4
n=15
r=common ratio=3


`S= (4(1-3^(15)))/(1-3)`

`S= (4(1-14348907))/(-2)`
S=-2(-14348906)
S=28697812

it adds to 28697812