Question

Find the number of terms of the geometric progression 81, 27, 9,....,1/81

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Answer 1

9

Explanation:

r = 27/81 = 1/3

a = 81

Tn = 1/81

ar^(n-1) = 1/81

81(1/3)^(n-1) = 1/81

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

(1/3)^(n-1) = 1/3^(8)

Compare the exponents,

n-1 = 8

n = 9