How do you find a formula of the nth term for this sequence: 1, 3, 9, 27, 81, …?

1 Answer
MeneerNask
Feb 12, 2016

Apparently the common ratio is #3#

Explanation:

The 2nd term is #3#, the 3rd=#9=3^2#, the 4th=#27=3^3#
To get to the #n#th term we will have to multiply #n-1# times by #3#

Or:
#t_n=3^(n-1)#

Watch out!
Usually the first term is called #t_0#, which would change the formula into #t_n=t_0*3^n=1*3^n#.
But then the #n#th term would be #t_(n-1)# and all would still be correct. Watch this when you're doing a test!

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