Geometric Series question (1 Viewer)

[Lucas_]

Hey,
I'm struggling to do the log bit of this solution. My worked guideline is unclear:

Which term of 54 + 18 + 6 + ... is equal to 2/243

Thanks

 

[iBibah]

Hey,
I'm struggling to do the log bit of this solution. My worked guideline is unclear:

Which term of 54 + 18 + 6 + ... is equal to 2/243

Thanks

ar^(n-1)=2/243

54.1/3^(n-1)=2/243

1/3^(n-1)=1/6561

Then type in you calculator:

log(1/6561)/log(1/3)=8

n-1=8

n=9