81, 27, 9, find the common ratio of the given sequence, and write an exponential function which represents the sequence. use n = 1, 2, 3, a) 3; f(n) = 81^n-1 b) 3; f(n) = 81(3)^n-1 c) 1 /3 ; f(n) = 81(3)^n-1 d) 1/ 3 ; f(n) = 81(1 /3 )^n-1answer -since each term is multiplied by 1/3to get to the next term, the common ratio is 1/3. the common ratio is also the base of anexponential function. the correct answer is1/3; f(n) = 81(1/3)^n-1so d.