How can i find the first term of a geometric sequence

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How can i find the first term of a geometric sequence when the common ratio is 3 and the fifth term is 972

Guest Dec 17, 2014

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Best Answer

A formula for the n^th term of a geometric sequence is: t_n = a·r^n-1

where a is the first term, n is the number of the term, and r is the common ratio.

If the fifth term is 972 and the common ratio is 3 ---> t₅ = 972 and r = 3:

t₅ = a·3^5-1 ---> 972 = a·3⁴ ---> 972 = a·81 ---> a = 972/81 = 12

geno3141 Dec 17, 2014

geno3141 · Answer 1 · 2014-12-17T06:02:40

A formula for the n^th term of a geometric sequence is: t_n = a·r^n-1

where a is the first term, n is the number of the term, and r is the common ratio.

If the fifth term is 972 and the common ratio is 3 ---> t₅ = 972 and r = 3:

t₅ = a·3^5-1 ---> 972 = a·3⁴ ---> 972 = a·81 ---> a = 972/81 = 12